How to make this create an explosion?

Go to this link: Explosion Damage. It will give you everything you need. Hope this helped!

Well this would be how to create the explosion. I'm kinda lost on how to make the damage part.

ball = script.Parent
damage = 25



function onTouched(hit)
    local humanoid = hit.Parent:findFirstChild("Zombie")
    E=Instance.new("Explosion",game.Workspace)
    E.Position=humanoid.Position
    E.BlastPressure=0
    E.BlastRadius= --Enter what you want here.

    if humanoid ~= nil then
        tagHumanoid(humanoid)
        humanoid.Health = humanoid.Health - damage
        wait(2)
        untagHumanoid(humanoid)
    end

    connection:disconnect()
    ball.Parent = nil
end

function tagHumanoid(humanoid)
    -- todo: make tag expire
    local tag = ball:findFirstChild("creator")
    if tag ~= nil then
        local new_tag = tag:clone()
        new_tag.Parent = humanoid
    end
end


function untagHumanoid(humanoid)
    if humanoid ~= nil then
        local tag = humanoid:findFirstChild("creator")
        if tag ~= nil then
            tag.Parent = nil
        end
    end
end

connection = ball.Touched:connect(onTouched)

wait(0.8)
ball.Parent = nil