1. **State the problem:** Calculate the value of the expression $15 + 4 \times 5$. 2. **Recall the order of operations:** According to the order of operations (PEMDAS/BODMAS), multiplication is performed before addition. 3. **Apply multiplication first:** Calculate $4 \times 5 = 20$. 4. **Perform addition:** Now add $15 + 20 = 35$. 5. **Final answer:** The value of the expression $15 + 4 \times 5$ is $35$.