its 23 over 45
2 1 18 5 23
- + - = -- + -- = ----
5 9 45 45 45
you have to make the ''bottom number'' the same in 2 of the equations so for 1st one you times it by 9 (dont forget to times the top by 9 aswell) 2nd one you times it by 5 (also times top by 5)
basicly what ure doing is you times the 1st equation by the bottom number of the 2nd one
and in the 2nd one you times the 2nd equation by the bottom number of the 1st one
tell me if my explanation wasnt good enough so i can help you even more
