If a matrix equation $\displaystyle AX=B$ has two solutions then why does it have infinitely many solutions?

Clue: if $\displaystyle X_1$ and $\displaystyle X_2$ are solutions then look into $\displaystyle X_3=sX_1+tX_2 (s,t\in R)$

Now, I really don´t know where to start on this one. I would appreciate some help just to get started.