3·x / (x + 8) + 5·x / (x + 2)
= 3·x·(x + 2) / ((x + 8)·(x + 2)) + 5·x·(x + 8) / ((x + 8)·(x + 2))
= (3·x·(x + 2) + 5·x·(x + 8)) / ((x + 8)·(x + 2))
= (3·x^2 + 6·x + 5·x^2 + 40·x) / ((x + 8)·(x + 2))
= (8·x^2 + 46·x) / ((x + 8)·(x + 2))
= 2·x·(4·x + 23) / ((x + 8)·(x + 2))