A parking lot charges $2 per hour for the first 4 hours

Plz hurry evaluate the expression a+b where a=8 and b=19

Serena is making an experiment. for that, she needs 20 grams of a 52% solution of salt. she has two large bottles of salt water: one with 40% and the other with 70% of salt in them. how much of each must she use to make the solution she needs? i am in need of

Olga bought a new skirt that cost $20. sales tax is 5%. how much did olga pay, including sales tax? 7.