Okay first you need to combine like terms together (3x and 1x)
7x + 4 = 5 + 4x
now you need x only on one side, you could subtract either 7x or 4x
3x + 4 = 5
subtract 4 over
3x = 1 is the answer
The answer is c because if you add 2 sides and the two sides are greater than the third than the triangle is possible
The answer is d because you just need to multiply AB by 4