Eve took one of her friends out to lunch. The lunches cost $100 and she paid 3% sales tax. If Eve left a 15% tip on the $100, how much in total did she pay?

Figure out two parts separately, tax and tip.
Tax: 3% = 3/100= 0.03
So 0.03 X $100 = $3 in tax
Tip: 15% means 15/100 = 0.15
0.15 X 100 = $15
So tax was $3, tip was $15, and bill was $100, all added up is $118

The linear equation is: y=ax+b