Let's call x the angle.
Remember that its complement refers to the difference 90 - x, since complementary angles sum 90°.
Having said that, we express the following expression.

Notice that we multiplied its complement by 3 to make it triple, then we subtracted 51 since the angle x is 51 less.
Let's solve for x now

Therefore, one angle is 43.8°, let's find its complement.

Therefore, the second angle is 46.2°.