17/80 = p/100
p = 17/80 * 100
p = 0.2125 * 100
p = 21.25
If you're taking trig, the "sum and difference formulas for trig functions" are basic facts that you'll need to learn and commit to memory. I'd suggest you look up these formulas on the net. You will likely immediately find listings for the sine, cosine and tangent.
Collect like terms and you'll get -2 - 3(a - b)
