Answer:
60 = n
Explanation:
This problem can be rewritten as:
18 is 30% of what?
% means "out of 100" and of means "multiply"
18 = 30/100 ⋅ n
100/30 ⋅ 18 = 100/30 ⋅30/100 ⋅ n
1800/30 = 100/30 ⋅ 30/100 ⋅ n (both the 30/100 and 100/30 are crossed out here)
60 = n
Ryan must do a total of 60 problems
Having done 18 problems already he has 42 remaining.