The question is telling you that the length of the rectangle is 3 metres more than twice the width.
So let:
w= width
L= length
Because the length is 3 metres more than twice the width: L= 2w+3
They also tell you the perimeter is 48 metres.
P= L+L+w+w
So the equation of the perimeter is:
48= (2w+3)+(2w+3)+2w +2w
48= 2(2w+3) + 4w
To find w, expand and simplify.
48= 4w+6+4w
48= 8w + 6
42= 8w
5.25=w
Now that you know the width, plug in the value into the length equation:
L= 2w+3
L=2(5.25)+3
L=10.50+3
L=13.5
If I am wrong let me know! I hope this helps.