a) 1400 : 20 - (17 + x) = 20
70 - (17 + x) = 20
17 + x = 70 - 20
17 + x = 50
x = 50 - 17
x = 33
b) 8 \(\times\) (x + 15) = 640
x + 15 = 640 : 8
x + 15 = 80
x = 80 - 15
x = 65
c) x \(\times\) 62 + x \(\times\) 38 = 4200
x \(\times\) (62 + 38) = 4200
x \(\times\) 100 = 4200
x = 4200 : 100
x = 42
d) x \(\times\) 186 - x \(\times\) 86 = 3400
x \(\times\) (186 - 86) = 3400
x \(\times\) 100 = 3400
x = 3400 : 100
x = 34