Question

[936-(32x25+a)]:[10+(49:7+2x4)]=28:7

Answer 1

[936-( 32 x 25 + a)] : [10 + ( 49 : 7 + 2 x 4)] = 28:7
[936 - ( 800 + a)] : [ 10 + ( 7 + 8 )] = 4
[ 936 - ( 800 + a)] : (10 + 15) = 4 
[ 936 - ( 800 + a)]  : 25 = 4
936 - ( 800 + a) = 4 x 25 
936 - ( 800 + a) = 100
800 + a= 936 - 100
800 + a = 836
a = 836 - 800
a = 36

Verific:
[936 - ( 800 + 36) ] : 25= 4
= (936 - 836) : 25 =
= 100 : 25 =
=  4