Math problem solving

Sam got $2.72 in change from a $20 music store gift certificate.He paid 8% in tax.what did he spend before tax?

3times the amount of black paint tubes plus 2 is equal to five 5 times the amount of white paint tubes minus 4. Find the amount of pain tubes.

8 pt to quarts =

One cell phone service charges $.10 per minute with no activation fee. Another cell phone service charges $.05 per minute with activation fee $20.Find the number of minutes for which the two cell phone service charges the same amount.

A brother and sister wanted to treat their mother to a birthday massage. the cost of the massage was $72 including a 20% tip.How much was the total bill before the tip?