3a - 2a x 4a + 6a
Using the order operations : Brackets, Exponents, Multiplication/Division, Addition/Subtraction.
=> We do the multiplication first : 2a x 4a = 8a^2.
-> = 3a - 8a^2 + 6a.
Now, we reposition the terms :
3a - 8a^2 + 6a = (3a + 6a) - 8a^2 = 9a - 8a^2.
Therefore, the answer is C.