Change the 15 1/3 to an improper fraction (46/3). Next multiply this by (3/4).
(46/3)(3/4) = 46/4 = 23/2 = 11.5 gallons was used to water the plants
15 1/3 - 11 1/2 = 46/3 - 23/2 = 92/6 - 69/6 = 23/6 = 3 5/6 gallons of water are left in the barrel
we can factor the whole thing:
(2sin(x) -1)(sin(x)+1) = 0.
Therefore, sin(x) = -1 and sin(x) = 1/2.
For the first one x = 3π/2 and the second is π/6 and 5π/6
So 3π/2, π/6 and 5π/6 are the solutions.
I do kind of have a problem with this because it doesn't mention if you should go over 360°. Otherwise, you have to add in an 2nπ into the equations like 3π/2 + 2nπ; 
but I don't know if that is necessary for you.
Answer:
10
Step-by-step explanation:
given

we first need to simplify the expression before we find it's value when s=-3
positive times negative=negative
so the equation becomes

substituting s=-3 into the equation.

=

=the negatives cancel out leaving

I believe it would be done like this:
subtract 2x-8 from both sides. then use cubric formula.
answer should be x= 1.688242