1188:[248-(974-6a)+15]x47=564
1188:[248-(974-6a)+15]=12
12×[248-(974-6a)+15]=1188
248-(974-6a)+15=99
248-(974-6a)=84
84+(974-6a)=248
974-6a=164
6a+164=974
6a=810
a=135
