Hello!
Let's change it to an equation.
[tex]5x - 10 = 900[/tex]
Switch the equation around
[tex]900 = 5x - 10[/tex]
First add 10 from 900
[tex]900 + 10 = 910[/tex]
[tex]5x = 910[/tex]
Divide both sides by 5
[tex] \frac{5x}{5} = \frac{910}{5} [/tex]
[tex]\framebox{x = 182}[/tex]