System of Equations word problem, Help

"A computer parts company wants to make a rectangular memory board that has
the perimeter of 28 cm and a diagonal length of 10 cm.
What are the demensions of the board?"

I need help defining the variables and figuring out the what the system of equations are

2l+2w=28
l^2+w^2=10^2

2w=28-2l
w=-l+14

l^2+(-l+14)(-l+14)=100
l^2+l^2-28l+196=100
2l^2-28l+96=0
2(l^2-14l+48)=0
2(l-6)(l-8)=0
l=6 or l=8

2l+2w=28
2(6)+2w=28
12+2w=28
2w=16
w=8

(6,8)
(8,6)