solution
in a right angle triangle all angles are = 90
but since they did not give us any angle, we should know that the two angle that will make up 90 will be 45
so it will be = tan 45 = a
15
15tan45 = a
a = 15
so now x^2 = 15^2 + 6^2
x^2 = 225 + 36
x^2 = 261
x = 16.2