where A is the first value, B the second value and x the percent
we can solve x
[tex]\begin{gathered} \frac{x}{100}A=B-A \\ x=\frac{100\times(B-A)}{A} \end{gathered}[/tex]this is the equation
and this is the percent:
[tex]\begin{gathered} x=\frac{100\times(900-750)}{750} \\ \\ x=20 \end{gathered}[/tex]the percent is 20%