Question

6+[15-(8:a×7+7)]×5=8:(1×4)+3×3

Answer 1

6+[15-(8:ax7+7)]x5=8:4+9
6+[15-(8:ax7+7)]x5= 11
[15-(8:ax7+7)]x5=11 - 6
15-(8:ax7+7) = 5 : 5 
8:ax7+7 = 15 - 1
8:ax7 = 14 -7 
8:a = 7 :7 
8:a = 1
a = 1 x 8 
a = 8

Answer 2

6+[15-(8:ax7+7)]x5=8:4+9
                               =2+9
                               =11
[15-(8:ax7+7)]x5=11-6
15-(8:ax7+7)=5:5
8:ax7+7=15-1
8:ax7=14-7
8:a=7:7
a=8:1
a=8