W=2L-3
W*L=193
replace W with 2L-3: (2L-3)L=193
2L^2-3L-193=0
Cannot factor
are you sure the numbers are correct?
If it cannot be factored, use the quadratic formula to find out L, then you can find out W
use the Pythagorean theorem to find the diagonal. I don't see an easier way.
Make x=0 in the second equation, giving you y=-3. If you plug that in to the top equation you would get x-3(-3)=-19, x+9=-19,x=-28.