Question

Show me how to solve this equation
2a - 3b = 21. B=3 - a

Answer 1

Assuming B means b, substitute b = 3 − a into 2a − 3b = 21.

2a − 3(3 − a) = 21
2a − 9 + 3a = 21
5a − 9 = 21
5a = 30
a = 6

Then b = 3 − a = 3 − 6 = −3.

Solution: a = 6, b = −3 (check: 2·6 − 3·(−3) = 12 + 9 = 21).