1)
xy + xz + xt = 1331
x = 11
11y + 11z + 11t = 1331
11(y + z + t) = 1331
y + z + t = 1331 / 11 = 121
2)
a - b = 15
x = 10
a) 2a-2b =
= 2(a - b) = 2 × 15 = 30
b) 3xa - 3xb =
3x(a - b) = 3 · 10 · 15 = 450
3)
ab = 20
bc = 10
b(a + c) = ab + ac = 10 + 20 = 30