what does x equal when 3x + 2y=4

3x+2y=4           (remove 2y from both sides)

3x=4-2y            (divide by 3 on both sides)

x=(4-2y)/3

This expression isn´t equal to a specifik number as long as you don´t know what number y is. 

This is the equation of a line......thus, there are infinite "solutions"....see the graph, here.....https://www.desmos.com/calculator/9dsvkv1kjf