The answers are boxed the rest of it is just the work in case you want to know how to do it.
Answer:
(x, y) = (3, 5)
Step-by-step explanation:

Solving by elimination here again, there are 2 good options available. Either multiply the whole bottom equation by -1 to cancel the x, or by 2 to cancel the y. I'll do the latter:

Add from top to bottom:

Now, with the value of x, solve for y in either of the equations. I'll choose the second one here:

(x, y) = (3, 5)
Answer:
d≈7.07
Step-by-step explanation:
Using the formulas
P=4a
d= \sqrt{2} a
Solving ford
d= \sqrt{2} P/4=2·20
/4≈7.07107