During 7 hours: 28 parts assembled
during 14 hours: 56 parts assembled
during 21 hours: 84 parts assembled
during 28 hours: 112 parts assembled
during 35 hours: 140 parts assembled
I belive there is none because it lands on the origin for y.
I: 2x+y=5
II:3x+2y=4
start by eliminating y
-2*I: -4x-2y=-10
II: 3x+2y=4
add both equations together
-2*I+II: -4x-2y+3x+2y=-10+4
-1x=-6
x=6
insert x=6 into I:
2*6+y=5
y=5-12
y=-7
so the solution is x=6, y=-7

The last line is in vertex form, and can see the vertex is located at (2,1).