设铅笔x只,水笔y只,钢笔z只
0.1x+3y+4z=100
x+y+z=100
z=100-(x+y)
x,y,z:N
0.1x+3y+4(100-(x+y))=100
0.1x+3y+400-4x-4y=100
-3.9x-y=-300
y=300-3.9x>=0
3.9x<=300
x<=300/3.9=76.9
0<=x<=76