Since angle EFG and GFH forms a linear pair, this only means that the sum of the two is equal to 180°. That is:
EFG + GFH = 180
So,
4n + 25 + 3n + 15 = 180
7n + 40 = 180
7n = 140
n = 20
Therefore:
EFG = 4n + 25 = 105°
GFH = 3n + 15 = 75°