4/9*(2,7m-2 1/4n)-4,2*(5/7m-0,5n) если m= 15/81, n=-5 решите 20

4/9 *( 2,7* 15/81 - 2 1/4 * (-5)) - 4,2*(5/7 *15/81 - 0,5*(-5)) = -5 5/6
1) 2 7/10 * 15/81 = 27/10 * 5/27 = 1/2
2) 9/4 *(-5) = -45/4
3) 1/2 - (-45/4) = 47/4
4) 4/9 * 47/4 = 47/9
5) 5/7 * 15/81 = 75/567 = 25/189
6) 0,5*(-5) = -2,5
7) 25/189 - (-25/10) = 25/189 + 5/2 = 995/378
8) 4,2*995/378 = 42/10 * 995/378 = 199/18
9) 47/9 - 199/18 = (47*2 -199)/18 = - 105/18 = -35/6 = -5 5/6
ответ: при m=15/81, n= -5 выражение равно -5 5/6