Answer:
 length: 16 m; width: 13 m
Step-by-step explanation:
Write each of the statements as an equation. You know that the formula for the perimeter is ...
 P = 2(L +W)
so one of your equations is this one with the value of P filled in:
 • 2L + 2W = 58
The other equation expresses the relation between L and W:
 • L = W +3 . . . . . . . . the length is 3 meters greater than the width
There are many ways to solve such a system of equations. Since you have an expression for L, it is convenient to substitute that into the first equation to get ...
 2(W+3) +2W = 58
 4W +6 = 58 . . . . . . . simplify
 4W = 52 . . . . . . . . . . subtract 6
 W = 13 . . . . . . . . . . . .divide by 4
We can use the expression for L to find its value:
 L = 13 +3 = 16
The length is 16 meters; the width is 13 meters.