x . 5 + 122 + 236 = 633

x . 5 + 358 = 633

x . 5 = 633 - 358

x . 5 = 275

x = 275 : 5

x = 55

b) (x : 12) . 7 + 8 = 36

(x : 12) . 7 = 36 - 8

(x : 12) . 7 = 28

x : 12 = 28 : 7

x : 12 = 4

x = 4 . 12

x = 48

A = (a x 7 + a x 8 - a x 15) : (1 + 2 + 3 + ........ + 10)

A = [a x ( 7 + 8 - 15 )] : [ ( 1 + 9 ) + ( 2 + 8 ) + ( 3 + 7 ) + ( 4 + 6 ) + 5 ]

A = [a x 0] : [ 10 x 4 + 5 ]

A = 0 : 45

A = 0

B = (18 - 9 x 2) x (2 + 4 + 6 + 8 + 10)

B = (18 - 18) x [ ( 2 + 8 ) + ( 4 + 6 ) + 10 ]

B = 0 x [10 x 3]

B = 0 x 30

B = 0

a) 576 + 678 + 780 - 475 - 577 - 679

= 780 - 475 + ( 576 - 577) - ( 678 - 679)

= 305 - 1 - 1

= 303

b) (126 + 32)$\times$(18 - 16 - 2)

= (126 + 32) $\times$0

= 0

c) 36 * 17 * 12 * 34 + 6 * 30

= 36 * 17 * 6 * 2 * 34 + 6 * 30

= 6 * (36 + 17 + 2 + 34 + 30)

= 6 * 119

= 714