Answer:
42 by 82 meters
Explanation:
The sum of the length and width is half the perimeter, so you have the simultaneous equations ...
x + y = 124
xy = 3444
I find it convenient to solve these equations graphically (see attachment). By hand, you are looking for factors of 3444 that sum to 124. You are not interested in any factor pairs with numbers greater than 124, so the relevant choices are ...
3444 = 28×123 = 41×84 = 42×82
Of these, only the last pair totals 124.
The school yard is 42 meters by 82 meters.