The interior angles of a triangle must add up to 180 eighty degrees.
Since the ratio is 7:5:3, let's say that the three angles have degrees 7x, 5x, and 3x
7x+5x+3x = 15x = 180
-> x = 12
Therefore, the three angles are 7*12=84, 5*12=60, 3*12=36 degrees.