beginner question

I have


exp1:a1*s*h1=(h2-h1)/r1 +u;
exp2:a2*s*h2 = -(h2 -h1)/r1 - h2/r2;
a1=1;
a2=1;
r1=.5;
r2=1/3;
solve([exp2,exp1],[h1,h2]);

and this works but now I want to use the numerical values for a1 a2  r1 r2.

How do I get a final answer.
Thanks
Doug Stewart