Planning with Limtiting Factors- Minimsing costs

I am having a problem trying to solve the simultaneous equation in the Kaplan book Chapter 4. The questions is Test Your Understanding 7.

The Objective Function
Z=10x + 5y

The constraints
.18x + .03y >= 100 (end points: x3,333.3, y555.5)
.05x + .02y >= 50 (end points: x2,500, y1,000)
.02x + .05y .= 40 (end points: x800, y2000)
Non Negativity x>=0, y>=0

The end points on the graph are: (Y=3333.3 and Y=2000)

The inspection method used (solving)
A: x=0, y=3,333.3
z=10x+5y=10(0) + 5(3,333.)= 16,666.50

B: .18X+03y=100 and .05x + .02y=50
gives- x=238.1 and y=1,904.8
(How was this calculated? I tried subbing in y=3,333.3 and solving!)

C: .05x + .02y=50 and .02x + .05y=40
gives- x=809.5 and y=476.2
(Again trouble deciding how to calculate end figures here)

D: x=2,000 y=0
z=10(2,000) + 5(0)=20,000
(straightforward thankfully)

I know I am missing a simple point in solving Lines B and C. Perhaps I have left out some information from above. If anyone could help I would be very grateful.