Good Question!

After \(1\) hour;

X(Brenda) |----------4----------(Alex)

Let \(R = 10\)

(Brenda)------------------------X---------4------|--------(Alex)

Distance travelled by Brenda at \(10\) mph in time \(t\)= \(10t\)
Distance travelled by Alex at \(4\) mph in time \((t+1)\)= \(4 + 4t\)

We are given;
\(10t = 2(4 + 4t)\)
\(t = 4\)

Therefore, Alex must have travelled for \(5\) hours

Let's check the options;

A. R-4
\(10 - 4 = 6\)

B. R/(R+4)
\(\frac{10}{(10+4)} = \frac{5}{7}\)

C. R/(R-8)
\(\frac{10}{(10-8)} = 5\)

D. 8/(R-8)
\(\frac{8}{(10-8)} = 4\)

E. 2R - 4
\(2(10) - 4 = 16\)

Hence, option C