To calculate \( E[X^2] \), we use the formula for the expected value of the square of a random variable:
\(E[X^2] = \sum P(X) \cdot X^2\)
Substitute the given values: \[ E[X^2]
\(= \frac{1}{4} \cdot (-10)^2 + \frac{3}{4} \cdot 20^2\)
\(E[X^2] = \frac{1}{4} \cdot 100 + \frac{3}{4} \cdot 400\)
\(= 25 + 300 = 325\)
Thus, the correct answer is \(\text{(c)}. \)