Question 830624
Let a be the rate of the first train and b the rate of the second.
We're given the following:
10(a + b) = 850
a = b+5
Distribute or divide.  Since it's even, I'll divide each side by 10.
(a + b) = 85
Substitute the value for a
(b+5) + b = 85
Subtract 5 from each side
B + b = 80
Add bs
2B = 80
Divide each side by 2
B = 40
Since we're told that a = b+5, a must be 45.
.
Let's prove this by adding in the values, 40 & 45
In 10 hours, train a travels 400 miles (40*10)
In 10 hours, train b travels 450 miles (45*10)
400 + 450 does indeed equal 850 miles.