I need help with the below problems. I don't understand how to find the common denominator when there is a variable as a denominator.

How do I work this on paper?

1/2 + 2/x = 3/4

Another problem I need help with is the below. I was able to figure out the answer, which is 29/10 but if I plug that into x to check the problem I have no clue how to work that.

x+1 over 3 + x+2 over 7 = 2

Thanks for your time,

KN