What is the primary subtractive color complementary to red?

Is this a trick homework question? I don't believe there is a 100% truthful answer because a subtractive colour is made up of two primaries, and a primary colour is not subtractive any more than a subtractive colour is primary ("...primary subtractive colour..."). Neither can there be a "main" subtractive colour if we are to consider your use of the Word "primary" in your question to mean that.

The complementary colour to red is cyan, which is made up of blue and green in equal amounts.