Which expression could be used to solve this problem?

bart practices piano every day. first he practices songs for 20 minutes. then he practices scales for 15 minutes. how much time does bart practice piano in 3 days?

a.
3 × (20 – 15)

b.
20 × (15 + 3)

c.
3 × (20 + 15)

d.
20 × (15 – 3)

Suppose that sahil knows that 45 people with ages of 18 to 29 voted. without using a calculator, he quickly says then 135 people with ages of 30to 49 voted. is he correct? how might sohil have come up with his answer so quickly?

Norder to get a certain shade of blue paint, a mixer must have 5 parts white paint to 3 parts blue. if 4 gallons of paint must be mixed, how many gallons of white paint must be used?

Acollege is selling tickets for a winter fund-raiser. one day, krissa sold 14 adult tickets and 8 student tickets for a total of $376. the next day, she sold 7 adult tickets and 11 student tickets for a total of $272. krissa wanted to find the price of one adult ticket, a, and the price of one student ticket, s. she wrote and solved the following system of equations.