Find the missing side please !!

In the given right triangle base and hypotenuse are given, we have to calculate the length of perpendicular.
Applying Pythagoras theorem in the given triangle which states,
[tex] (Hypotenuse)^{2}=(Base)^{2}+(Perpendicular)^{2} [/tex]
[tex] (21)^{2}=(15)^{2}+(x)^{2} [/tex]
[tex] 441=225+x^{2} [/tex]
[tex] x^{2}=441-225 [/tex]
[tex] x^{2}=216 [/tex]
[tex] x=6\sqrt{6} [/tex]