Question

What is the value of a in the equation 3a + b = 54, when b = 9?

15
18
21
27

Answer 1

`\left \{ {{3a+b=54} \atop {b=9}} \right. \\\\Substitution\\\\ 3a+9=54\ \ \ | subtract\ 9\\\\3a=45\ \ \ | divide\ by\ 3\\\\ a=15\\\\ b=9`

Answer 2

`3a+b=54 \\\\ 3a+9=54 \\\\ 3a=54-9 \\\\ 3a= 45 \\\\ \boxed{a=(45)/(3)\to15}`