Which equation represents the statement?
juan's age, x, is 4 times his age 15 years ago.
x = 4x + 15
x = 4(x − 15)
x = 4 + 15x
x = 4x - 15

Amuffin recipe, which yields 12 muffins, calls for cup of milk for every 1 cups of flour. the same recipe calls for cup of coconut for every cup of chopped apple. to yield a batch of 30 muffins, how much flour will be needed in the mix?

The train station clock runs too fast and gains 5 minutes every 10 days. how many minutes and seconds will it have gained at the end of 9 days?

I'm at a bookstore with $\$35$ in my pocket and a $20\%$-off coupon. what is the cost of the most expensive book i can buy with my money and the coupon? (assume that there are books of every possible price in the bookstore. it's a large bookstore! )