Problem: What is (a) if 7x(a)+4x(a)=108?
Fred's age is 7 times Hans. Ralph's age is 4 times Hans.
Together they are 108. How old is each person?
Your equation doesn't include Han. If a = Han's age...
a + 7a + 4a = 108
12a = 108
a = 9
Han's age is 9.
Fred's age is 7 * 9 = 63
Ralph's age is 4 * 9 = 36
Together, they are 9 + 63 + 36 = 108.