rule

42x+30y≥252

0≤ x≤6(252/42=6)

0≤y≤9(252/30 rounded to the whole number)

M=300x+200y

In this case, find the minimum value of m:

Yes: y≥42/5-7/5x

Introduction: m ≥ 300x+200x (42/5-7/5x)

Finishing: M≥ 1680+20x

Because 0≤ x≤6, m is the minimum value when x=0, but y=9 when x=0, so the lowest rental fee is 1800 yuan.