It is known that the minimum square side length is 50 and the maximum square side length is x.
a=50
b=x
f=b-50=x-50
e=f-50=x- 100
c=e-50=x- 150
2)d=c
f+b=2c+e
x-50+x = 2(x- 150)+x- 100
2x-50=2x-300+x- 100
X = 400-50 = 350
3) Let Xiao Ming catch up with Xiao Hong for the first time after y minutes.
pq=mn=350+300=650
qm=pn=300+250=550
150*(4+y)+650=200*y
600+ 150y+650=200y
50y= 1250
Y=25 minutes
Xiaoming ran away.
200 * 25 = 5000m
5000/(650 * 2+550 * 2) = 5000/2400 = 200m.
So at this moment they are on the edge of the rectangle pq.