We can use the given points to construct the equations for the mail truck's and fire truck's motion.
Mail truck:
slope = (9 - 3) / (1 + 5)
slope = 1
y - 9 = (x - 1)
y = x + 8
Fire truck
slope = (2 - 12) / (0 + 10)
slope = -1
y - 12 = -1(x + 10)
y = 22 - x
Equating the two:
x + 8 = 22 - x
2x = 14
x = 7
y = x + 8
y = 7 + 8
y = 15
The trucks intercept at the point (7, 15)