Answer: D. $245$

Explanation:1. **Understand the problem:** We need to find the value of the function $f(x)$ when $x$ is equal to $7$.

2. **Substitute $x=7$ into the function definition:** The function is $f(x) = 5x^2$. Replacing $x$ with $7$: $f(7) = 5(7)^2$

3. **Evaluate the expression:** First, calculate $7^2$: $7^2 = 7 \times 7 = 49$. Now, multiply by $5$: $f(7) = 5 \times 49$ $f(7) = 245$.

4. **Conclusion:** The value of $f(7)$ is $245$.