I keep getting .0008 when the answer is .00008 (four zeros)

x²=3.39*10^-7 *0.02
x²=33.9*10-6 *0.02
x^2 = 0.678 *10^-6
x=0.8 *10^-3
x=0.0008
That answer is wrong, but I don't know why. Putting the expression in a sci.calculator, I get four zeros between the point and the eight.

Could you tell where's my mistake?

Your mistake is in the very first step! If x²=3.39*10^-7 *0.02, then:

x²=33.9*10^-8 *0.02

Since 33.9 is 10x bigger, 10^-7 must get 10x smaller.

I always found it easier to convert everything into scientific notation first. For example:

x² = 3.39*10^-6 * 2*10^-2
x² = 6.78*10^-8

Hope this helped!

then just use the correct anwserr ! duhhhhhh ! if you know the anwser why does it matter