Suppose you wish to express $\sin(3t)$ in terms of $\sin t$ and $\cos t$. Apply the sum formula to $\sin(3t) = \sin(t+2t)$ to obtain an expression that contains $\sin(2t)=\sin(t+t)$ and $\cos(2t)=\cos(t+t)$. Apply the sum formulas to those two expressions. Enter the resulting expression for $\sin(3t)$ here
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using upper case S to denote $sin t$ and upper case C to denote $\cos t$. For example, if your answer was $3\sin t \cos t$ you'd simply enter 3*S*C. Remember that WeBWorK (and mathematics) is case sensitive! You may be able to find an equivalent expression for $\sin(3t)$ in the literature, but WeBWorK will not recognize the equivalence. You have to follow the procedure outlined above.
Hint: Apply suitable sum formulas twice.