a. (8x5+6x9+X):9+312=323
(40+54+x):9+312=323
(94+X):9=323-312
94+X=11x9
x=99-94
x=96
b.4x[(4xX-72):4+20]-64=20
4x[(4X-72):4+20]=84
(4X-72):4+20=84:4
(4x-72):4=21-20=1
4x-72=4
4x=4+72=74
x=74:4
x=18.5
c.100-[250-5x(5-x):5]x3=40
[250-5x(5-x):5]x3=140
250-5x(5-x):5=140:3
d. 643-[(x-162):5+159]=454
(x-162):5+159=1097
(x-162):5=938
x-162=4690
x=4852
