Answer: [tex]a + \frac{1}{4}b[/tex]
This is the same as [tex]a + \frac{b}{4}[/tex]
All we're doing is adding 'a' and [tex]\frac{1}{4}b[/tex] since the term "sum" is the result of adding two or more numbers.
One quarter of a number is the same as dividing by 4.
Example: one quarter of 28 = [tex]\frac{1}{4}*28 = \frac{28}{4} = 7[/tex]