How to Add air resistance to my equation?

my equation is stated below, it calculates the distance the ball is required to travel, and increase the velocity dependent on the distance, however i am making a basketball game, that has varied air resistance due to different locations, it says that i am "attempt to perform arithmetic (mul) on number and Instance"

local t = 1;
local mouse = game.Players.localPlayer:GetMouse();
local hrp = game.Players.LocalPlayer.CharacterAdded:Wait():WaitForChild("HumanoidRootPart");
local bball = game:GetService("ReplicatedStorage").ball;
local active =false
local speed = 100

mouse.Button1Down:connect(function()
    if active == false then
        active = true
        local tar = (mouse.hit.p - game.Players.LocalPlayer.Character.HumanoidRootPart.Position).magnitude
        if tar < 50 then 
            t = 1
        elseif tar >60 and tar< 90 then 
            t = tar/speed
        elseif tar >90 then
            t = 4
        end
        local g = Vector3.new(0,-game.Workspace.Gravity,0)
        local x0 = hrp.CFrame *Vector3.new(0,2,-2) -- setting the position for starting place of the ball



        --calculate the v0 needed to reach mouse.hit.p

        -- local v0 = (mouse.hit.p - x0 - 0.5*g*t*t)/t -- the calculation to find initial velocity needed to reach a certain target in a given time

        -- have the ball travel the path
        local rho = 1.2 --density of air
        local r = 0.017 --area of item
        local c = 0.47 -- drag coefficient
        local A = math.pi*r^2
        local v0 = (mouse.hit.p - x0 - 0.5*g*t*t)/t 
        if tar/10 >2 then
            game.Players.LocalPlayer.Character.Humanoid:ChangeState(Enum.HumanoidStateType.Jumping)
            wait()
            game.Players.LocalPlayer.Character.Humanoid:ChangeState(Enum.HumanoidStateType.Landed)
        end
        local c = bball:Clone();
        c.Velocity = v0 - 0.5*rho*A*c*(v0).magnitude^2*v0;
        c.CFrame = CFrame.new(x0);
        c.CanCollide = true;
        c.Parent = game.Workspace
        wait(t)
        active  =false
        print(tar)
        print(t)
        t = 1
    end
end)

thankyou in advance :)