Mike had 3/4 as many comic books as Robert. When Robert gave half of his comic books to Mike, he then had 30 fewer comic books than his friend. How many comic books did Robert have at first?

Call thee number that Robert had intially, N

Then Mike had (3/4)N

When Robert gives away 1/2 of his we have that

N - (1/2) N + 30 = (3/4)N + (1/2)N simplify

(1/2)N + 30 = (5/4)N

(5/4)N - (1/2)N = 30

(3/4)N = 30

N = 30 * (4/3) = 40 = the number that Robert had initially