We need to find x, that is, the measure of the diagonal. To do this, we notice that we have a right triangle, and thus, we can apply the Pythagorean theorem. Then, we have
![\begin{gathered} x=\sqrt[]{(30\operatorname{cm})^2+(24\operatorname{cm})^2} \\ x=38.42\operatorname{cm} \end{gathered}]()
Rounded to the nearest centimeter, we see that the size of the monitor is 38cm