Carlos pays a monthly fee of $6$6. In a mathematical function, this would be represented by a constant of 66.
He also pays 88 cents, or $0.08$0.08, per minute spoken. If xx were the number of minutes spoken, this would be represented by 0.08 x0.08x.
Overall, Carlos' long distance bill can be represented by the function:
f(x) = 0.08 x + 6f(x)=0.08x+6; where f(x)f(x) is the long distance bill, and xx is the number of minutes spoken.
Last month, his long distance bill was $18.64$18.64.
Let's replace f(x)f(x) with 18.6418.64:
Rightarrow 18.64 = 0.08 x + 6⇒18.64=0.08x+6
If we solve for xx, we will find the number of minutes for which Carlos was billed:
Rightarrow 12.64 = 0.08 x⇒12.64=0.08x
Rightarrow 158 = x⇒158=x
therefore x = 158
Therefore, Carlos was billed for 158 minutes.