(8 × 13 + 20 × 6 ) + a + 56 : 7 = 300
( 104 + 120 ) + a + 8 = 300
224 + a + 8 = 300
a + 232 = 300
a = 300 - 232
a = 68
24 : 3 × 45 - a - ( 20 × 4 : 10 + 81 : 9 ) = 156
8 x 45 - a - ( 80 : 10 + 9 ) = 156
360 - a - ( 8 + 9 ) = 156
360 - a - 17 = 156
360 - a = 156 + 17
360 - a = 173
a = 360 - 173
a = 187
a × 5 + 63 : 9 × 100 - (18 × 15 - 11 × 23 ) = 703
a × 5+ 700 - ( 270 - 253 ) = 703
a × 5 + 700 - 17 = 703
a × 5 + 700 = 703 + 17
a × 5 = 720 - 700
a × 5 = 20
a = 20 : 5
a = 4