Precalculus, Chapter 5, 5.4, Section 5.4, Problem 40

It is in the form of (tan A + tan B)/(1 - tan A * tan B)
that is equal to tan (A + B)
It is clear from the question, that A = 25^0 , B = 110^0
therefore tan(A+B) = tan(25^0 + 110^0)
= tan(135^0)
= tan(pi - 45^0)
= - tan(45^0)
= -1