Analysis: According to the meaning of the question, the solution of equation 5a+x= 13 is x=-2, so we can find a=3 first, and then substitute it into the original equation to solve it.

Answer:

Solution: From the meaning of the question, 5a-2= 13,

Solution, a=3,

∴ The original equation is 15-x= 13,

Solution, x = 2；;

So choose C.