If the width is 6.5 then double that to work out the two widths which would be 13. Take that from the perimeter so you're left with 21. Half 21 to work out one length which is 10.5. Length = 10.5
It’s 40 you do bast times height divided by 2
7^2 = 6^2 + 9^2 - 2(6)(9)cos(m)
-68 = 2(6)(9)cos(m)
cos(m) = -0.6296
m = arcos ( -0.6296)
m = 129.0 degrees
56 is you answer you need.
