I've been looking for an example or documentation on how to have a quesiton where the answer is a vector with variable entries, but so far I haven't been successful.

The context in my case is linear transformations. I want students to find a formula for a linear transformation from R2 to R2, and I want to format the problem like T(x,y) = __________________

rather than T(x,y) = (_____x + _____y, _____x + _____y)

and have students enter an answer like (3x+2y, -x+4y). The vector math object doesn't seem to like entries that are formulas.