Question 6511
1. Let side 1 = x, side 2 = x + 5, and side 3 = 2(x + 5) - 20.
All of the 3 sides added together have to equal 75. Therefore:

x + x + 5 + 2(x + 5) - 20 = 75
4x + 15 - 20 = 75
4x = 80
x = 20

Therefore, side 1 = 20 m, side 2 = 25 m, and side 3 = 2(20 + 5) - 20 = 30 m.

2. Let the width of the rectangle = w and the length of the rectangle = l.
Therefore, l = 2w + 6. A rectangle has two lengths and two widths. As such, the perimeter of a rectangle is 2l + 2w, which you are told in the question equals 84.
2l + 2w = 84
2(2w + 6) + 2w = 84
4w + 12 + 2w = 84
6w = 72
w = 12
l = 2(12) + 6 = 30

I'll let you work out the last two by yourself because these questions ALL work on the same principle.
Good luck and if you need any further help, just submit another question :).
Regards,
-Mike