Hi there!
Okay, this i very easy. All you need to do is divide 7 by 42 to see what your x value is.
I'd divide both sides by 7, though.
It would look like this:
7x/7 = 42/7
x = 6.
Your answer is A, 6 = x.
When in doubt of your answer you can easily slip the 6 into the x's place, since x in the equation is 6. It would look like this:
7 × 6 = 42.
Hope this helps! :)