The area of a square is defined by the formula
A = s²
where A is the area and s is the length of one side
you are given with the following data
 \frac{ds}{dt} = 5 m/min
s = 6m
since this involves the change of area as to time then having the area differentiated you'll have:
A = s^2
 \frac{dA}{dt} = (2s)  \frac{ds}{dt}
substituting the given you'll have:
 \frac{dA}{dt} = 2(6m)(5m/min)
 \frac{dA}{dt} = 60 m^2/min