you can also write this as the following:
x-10=90/3
then you can solve it
x-10=30
then you solve this equation
so you add 10 to both sides because you have to do the inverse operation
then you would end up with x=40
you can also check this to see if your answer is right
you plug in 40 for x
you would have something similar to this
40-10=90/3
30=30
so 40 is right
40 is the final answer