a= 6 × 7 - 5 × 6 - 72 : 8
= 42 - 30 - 9
= 12 - 9
= 3
b = 64 : 8 +3 × 4 - 4 × 4
= 8 + 12 - 16
= 20 - 16
= 4
c = 42 : 6 - 16 : 8
= 7 - 2
= 5
3 × a - 2 × b + c = 3 × 3 - 2 × 4 + 5
= 9 - 8 + 5
= 1 + 5
= 6
