1/4 yard. There isn't much more of a way to explain it. Its just remembrance for this
Prime factorization for 600 is 2^3 times 3 times 5^2
The price of each ticket will be the slope found from the data.
Slope=m=(y2-y1)/(x2-x1)=(177.5-146.25)/(18-13)
m=6.25 (so the cost of the tickets is $6.25)
Now we can use any data point to solve for b, or the y-intercept of the line:
y=6.25x+b, using (177.5, 18)
177.5=6.25(18)+b
b=$65.00d
So he started with $65.00