Find measure GM round to nearest hundredth

Which values for a and b will create infinitely many solutions for this system of equations? ax-y=8 2x+y=b

Express the following as a function of a single angle. cos(60) cos(-20) - sin(60) sin(-20)

Apackage of five erasers cost 0. $.39 at this rate how many how much would 60 erasers cost in dollars and cents