You have to distribute the minus sign to the second parenthesis, changing the sign of every term:

Answer:
c = -1
Step-by-step explanation:
3(c+5)=12
3 × c = 3c
3 × 5 = 15
3c + 15 = 12
<u> - 15 -15</u>
3c = -3
c = -3 ÷ 3 = -1
Check:
3(-1+5)=12
-3 + 15 = 12
Answer:
tax: $18.9
total cost: $333.9
Step-by-step explanation:
$315 × 0.06 = 18.9
18.9 + 315 = 333.9
btw you can also do "315 × 1.06" to get the total cost without having to manually add the tax
It is 2/18 I hope I can help