Подобные слагаемые. ⁸/₁₅ ( 3 ³/₄m - ⁵/₁₆ n) - ³/₂₀ ( 6 ²/₃m - 4 ⁴/₉n) =

8/15* ( 15/4m - 5/16n ) - 3/20* ( 20/3m - 40/9n ) = 8/15*15/4m - 8/15*5/16n - 3/20*20/3m + 3/20* 40/9n = 2m - 1/6n - m + 2/3n = m + 3/6n или m + 1/2n

3 3/4m = 15/4m
6 2/3m = 20/3m
4 4/9n = 40/9n
8/15•( 15/4m - 5/16n ) - 3/20•( 20/3m - 40/9n ) = 8/15*( 15/4)m - 8/15*(5/16)n - 3/20*(20/3)m + 3/20*( 40/9)n = 2m - (1/6)n - m + (2/3)n = m - (1/6)n + ( 4/6)n = m + (1/2)n = 
= m + 0,5n