5+3x=4x
only when
x=5
The two expression are only equal at x=5
Answer:

Step-by-step explanation:

Divide 3 on both sides:

Add 1 to both sides:

Multiply by 7 on both sides:

Answer:
D.
Step-by-step explanation:
She cannot buy a negative number of notebooks. She can buy 0 notebooks, or 1 notebook, or 2, or 3, etc. The number of notebooks she buys must be a non-negative integer.
Answer: D.