Question

a cell phone company charges $10 per month for up to 500 text messages and $0.15 for each additional text messages. Stanley was charged $14.50 last month for text messages. Write and solve an equation to find the number of text messages he sent and received last month.

Answer 1

Because he was charged more than $10, we can write the equation:

0.15*t+10=14.50

Where t is the amount of text messages over 500.

Alternatively, you could do:

0.15*(t-500)+10=14.50

Where t is the amount of text messages.  0.15 modifies t or t-500 because it's the cost for texts over 500, and 10 is added for the first 500 texts.  14.50 is on the other side because it's the total cost.