Answer:
x=9
Step-by-step explanation:
FE is 3x-7
since ΔABC≅ΔDEF the equivalent of FE is CB, or BC...which is 20
3x-7=20
3x=27
x=9
Brianna's thinking is incorrect.
Expessions A, and C. are equivalent.
For C, you add 5x and x together (because they have the same variable) to get 6x - 4.
For A, you subtract 9x and 3x (because they have the same variable) to get 6x- 4.
The only pairs for the greatest common factors of 5 are 1, 5