Amanda simplifies the following expression and shows her work below. What mistake did Amanda make that resulted in an incorrect answer?

34−8÷2 + 3∙4


34−4 + 3∙4


37 – 7 ∙ 4


34−28


6


a

She added before multiplying


b

She multiplied before dividing


c

She subtracted before adding


d

She added before dividing