X = 4.2(-2/7 + 2 2/3) - 15.6 + 8 3/5
1) -2/7 + 2 2/3 = 2 ( (-6 + 14)/21) = 2 8/21
2) 4.2 * 2 8/21 = 42/10 * 50/21 = 42*50 / (10*21) = 10
3) -15.6 + 8 3/5 = -15.6 + 8.6 = -7
4) 10 - 7 = 3
Составим пропорцию.
3 ---- 100%
у ---- 115%
у = 115*3/100 = 345/100 = 3,45
Ответ. 3,45.