Answer:
$52.44
Step-by-step explanation:
Long method:
1. Convert the percentage into a decimal (15/100 = 0.15)
2. Multiply the decimal by the cost of the haircut (0.15 x $45.60 = $6.84)
3. Add this product by the cost of the haircut ($6.84 + $45.60 = $52.44)
Quicker Way (easier w/ a calculator)
1. Add 100% to the percentage she wants to add (100% + 15% = 115%) You can also express this as a number (115/100 = 1.15)
2. Multiply this new percentage by the cost of the haircut (1.15 x $45.60 = 52.44)
In a single equation, it would be

Any number times 0 is going to equal 0
The car goes 23.2 miles every gallon, so with 15 gallons (15 * 23.2 = 348) it can go 348 miles. With the extra .25 that the car has, it can go 0.25 * 23.2 = 5.8 miles. 348 miles plus the 5.8 miles gets you 353.8 miles on 15.25 gallons.
.0562 is the smallest number