1. The problem is to evaluate the expression: $12 + 15 \div 3 \times 6 - 4$. 2. According to the order of operations (PEMDAS/BODMAS), division and multiplication are performed before addition and subtraction, and they are evaluated from left to right. 3. First, perform the division: $15 \div 3 = 5$. 4. Next, multiply the result by 6: $5 \times 6 = 30$. 5. Now the expression is simplified to: $12 + 30 - 4$. 6. Perform the addition: $12 + 30 = 42$. 7. Finally, subtract 4: $42 - 4 = 38$. 8. Therefore, the value of the expression is $38$.