HELP I NEEED EQUATIONS FOR 3 & 4!!

When using the linear combination metho e linear combination method to solve a system of linear equations, the four options are:

Ana drinks chocolate milk out of glasses that each holdof a liter. she has of a liter of chocolate milk in her refrigerator. 10 how many glasses of chocolate milk can she pour?

Can someone me with #s 8, 9, and 11. with just one of the three also works. prove using only trig identities.