Answer: [tex]a=7[/tex]
Reorder the terms
[tex]-15 + 3a = 6[/tex]
Solving for variable 'a'.
Move all terms containing a to the left, all other terms to the right.
Add '15' to each side of the equation.
[tex]-15 + 15 + 3a = 6 + 15[/tex]
Combine like terms: -15 + 15 = 0
[tex]0 + 3a = 6 + 15\\3a = 6 + 15[/tex]
Combine like terms: 6 + 15 = 21
[tex]3a = 21[/tex]
Divide each side by '3'.
[tex]a = 7[/tex]
