Answer:
80 miles per hour
Step-by-step explanation:
Eastbound
r = r - 12
t = 5 hours
d = d_e
Westbound
r = r
t = 5 hours
d_w = 850 - d
The two distances add up to 850 miles
d_w + d_e = 850 miles
(r * t)_w + ( (r -12)*5 ) = 850 miles
r*5 + (r - 12) * 5 = 850 Pull out 5 as a common factor
5 * ( r + r - 12) = 850 Divide by 5
(r + r - 12) * 5/5 = 850/5 Do the cancellation
2r - 12 = 170 Add 12 to both sides
2r - 12 + 12 = 172 + 12
2r = 184 Divide by 2
r = 92
r = the westbound train = 92 mph
r - 12 = The eastbound train = 80 mph
