What is the value of3x^2-7x+9 when x =4

15-6+7=16. The expression should be written as 15-(6+7).

Step-by-step explanation:

The sum of 6 and 7 is (6+7). 15 minus the sum of 6 and 7 would then be written as 15-(6+7), because this way you subtract the entire sum from 15. The expression 15-6+7 just subtracts 6 from 15, then adds 7 onto this number, which is not the same thing as subtracting 6+7 from 15.