The break-even point is given when:

In another words, when the costs are equal to the revenue. If this happens, the profit will be equal to 0. From the graph, the profit is equal to 0 for 60,000 units.
Answer:
B
in step 2 he made his first mistake
1/2(n-4)-3=3-(2n+3)
1/2n-4/2-3=3-(2n+3)
1/2n-2-3=3-(2n+3)
in the second step he put 5 instead of 2.
210 ÷ 6 = 35 miles to the gallon
280 ÷ 35 = 8 gallons for 280 miles