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 :)

thankyou, enes223 Appreciate the help.