The correct answer is 3.
The formula for the law of sines is the following:
P/sin P = Q/sin Q = R/sin R
So, if you break these up into two different equations, you will have:
P/sin P = Q/sin Q and P/sin P = R/sin R
To solve, get P alone on one side of the equation by multiplying the other side by sin P:
P = Q sin P/sin Q and P = R sin P/sin R
When you look at the answers, you'll see that the second equation is an option.