Find dimensions of the rectangle, pls !

The area of a rectangle is length x width so we can deduce that 
42 = length x width.

"the length of the rectangle is 5 yd more than twice the width"
Using this information we can figure out the value of the length in terms of the w (the width)
w = width
l = 2w + 5

Plug these values back into the original formula of length x width.
(2w + 5)w = 42
Distribute the w
2w^2 + 5w = 42
Subtract 42 from both sides
2w^2 + 5w - 42 = 0
Factor
(2w - 7)(w + 6)
w = 7/2 or -6
Since a measurement of something cannot be negative, the width must by 7/2.
Plug the value of w back into the l value.
2w + 5 = l
2 x 7/2 + 5 = l
7 + 5 = l
12 = l

Final  
Length: 12 yd
Width: 7/2 yd