Answer:
Step-by-step explanation:
[tex]x + 3 = 15[/tex]
Collect like terms and simplify
[tex]x = 15 - 3 \\ x = 12[/tex]
Substitute 12 for x into the equation
[tex]18 + 6x \\ 18 + 6(12) \\ 18 + 72 \\ = 90[/tex]