The sum of angles of a triangle is given by an expression 2a + b degrees, while that of a quadrilateral is given by 13a - b degrees. Calculate the values of 'a' and 'b.'
a) a = 15°, b = 5°
b) a = 10°, b = 8°
c) a = 20°, b = 10°
d) a = 25°, b = 7°