Question

What number should be substituted for the question mark to balance the equation and why is that the correct number?

UPDATE:The attachment shows the rest of the question and choices.

Answer 1

7

Answer 2

Thank you, that was what I thought it was.

Answer 3

Another question. Need help

Answer 4

So confused

Answer 5

From F=ma you can deduce 50N=a2kg and 25N=ma \(\rightarrow\) m=1kg