Using PEMDAS, u know to multiply 4 by 9 first which results in 45. Now comes adding or subtracting. We must work from left to right, therefore we add 45 and 6 first. U get 39 if u do the math. Then we must subtract 3 from 39 so ur answer should be 36.
You would use PEMDAS (Parenthesis, Exponents, Multiplication, Division, Addition, Subtraction). This means you would use multiplication first because it is before addition or subtraction. That means you would do 4*9 = 36. So now you have 36 + 6 - 3. Since the next step is adding, add 6 to 36, and you will get 42. Then subtract 3 from 42 to get your final answer of 39. Hope this helps. Let me know if you don't understand something, and feel free to ask more questions.
