Ответ:
а)
7x + 2x = x*(7+2) = 9x
11y - 3y = y*(11-3) = 8y
9a + 6a = a*(9+6) = 15a
13c - 3c = c*(13-3) = 10c
б)
3x * 5 * 10 = (3 * 5 * 10) x = 150x
4 * 2y * 15 = (4 * 2 * 15) y = 120y
70 * 50y * 2 = (70 * 50 * 2) y = 7000y
6a * 300 * 50 = (6 * 300 * 50) a = 90000a