
The cosine function is negative in 2nd and 3rd quadrants, So you know that you will have 2 solutions. One between pi/2 and pi, the other between pi and 3pi/2.
Refer to a unit circle to find that

Final Answer:
Answer:
a.1
b.10
c.120
Step-by-step explanation: don't know that last one
13.8 gallons
Rounded from 13.8462
The equation you would use is (65/18)=(50/x) solve for x