so i'm using the letter l for length w for width p for perimeter and a for area
l = 5w + 7
a = (5w+7) x w
p =2(5w+7) + 2w
= 10w + 14 +2w
p = 12w + 14
158cm = 12w + 14
12w = 144
w = (144/12) = 12
l = 5w + 7
so 5 x 12 + 7 = 67
width = 12cm length = 67cm
proven: area = 804cm^2 which is 12 x 67
hopes that u can understand my workings and that this helps :)