The question is a bit confusing but it looks like you are looking for
5% of x = 10
or you could write this as
x*5%=10
To solve this, convert the percentage to a decimal by removing the percent sign shifting two places to the left. One place would make this .5, in order to move it a second place we need to add a zero as a place holder and we get .05
We can rewrite this problem again as
.05x=10
Solve for x by dividing both sides of the equation by .05
x=200