a. Your variable is the number of miles that Steve runs (which I'll label as S; Kevin's distance is K)
b. The expression for Kevin would be:
S+4 = K ---> Why? Because it says that Kevin ran 4 more miles than Steve did. So, whatever value S is, K is always 4 more than that.
The expression for Steve would just be: S = S
c. The equation is: 4+S+S = 26. Why? Because since the two ran a total of 26 miles together, K+S = 26. But, we already figured out that K = S+4 (see b.). So, we can substitute 4+S for K into K+S=26 to get 4+S+S = 26.
d. Solving it:
4+S+S = 26 ---> 4+2S = 26 ---> 2S = 22 ---> S = 11
Solution: Steve ran 11 miles.
e. Checking: plug in 11 as S
4+2(11) = 26 ---> 4+22 = 26 ---> 26 = 26
And...it's in the domain they give you.
Final Answer: 11 miles
