Step 1: Understanding the Concept
Put \(u=x^{5}\), so \(x=u^{1/5}\). Then the relation becomes a formula for g in terms of u.
Step 2: Find g
\(g(u)=3x^{7}=3u^{7/5}\).
Step 3: Differentiate
\(g'(u)=3\cdot\frac{7}{5}u^{2/5}=\frac{21}{5}u^{2/5}\).
Step 4: Substitute
\(3125=5^{5}\), so \(u^{2/5}=5^{2}=25\).
\(g'(3125)=\frac{21}{5}\times 25=105\).
Final Answer:
g'(3125) equals 105.
\[ \boxed{\text{(C) }105} \]