(4 13/18-3 7 /9)*(1/2-4/17) = 19/68
13*1 - 7*2
(4 13/18-3 7 /9) = (4-3)+(13/18-7/9)= 1 + ------------------------ = 1+1/18= 1 1/18
18
1*17 - 4*2 17 - 8 9
(1/2-4/17) = ----------------------------- = ------------------- = -------------
34 34 34
1 1/18 * 9/34 = 19/18 * 9/34 = 19/68