B, 38 . x - x . 12 - x . 16 = 40
x ( 38 - 12 - 16 ) = 40
x . 10 = 40
=> x = 40 : 10 = 4
C, 165-(35 : x + 3) .19=13
(35 : x + 3) .19 = 165 - 13
(35 : x + 3) .19 = 152
35 : x + 3 = 152 : 19
35 : x + 3 = 8
35 : x = 8 - 3
35 : x = 5
x = 7
D, x+5.2-(32+16.3:16-15) = 0
x + 10 - 32 - 16 . 3 : 16 - 15 = 0
x - 22 - 48 : 16 - 15 = 0
x - 22 - 3 - 15 = 0
x = 0 + 15 + 3 + 22
x = 40