If 1=square foot -1, what is the value of i^3

I think you meant to say "root" instead of "foot". Also, I think you meant to use the letter i instead of the number 1 on the left side of the equation. It should be this:

i = square root of -1 = sqrt(-1)

Often it's handier to use the shortcut "sqrt" for "square root"

Let's square both sides of the equation given:

i = sqrt(-1)

i^2 = (sqrt(-1))^2

i^2 = -1 ... notice squaring the square root have the two cancel out and go away

Now multiply both sides by i

i^2 = -1

i^2*i = -1*i

i^2*i^1 = -i

i^(2+1) = -i

i^3 = -i

which is the final answer

the correct answer is 5 6 and 7