I want to learn how to do these types of problems
When you have a problem with 2 variables, there is an infinite number of possible solutions. FYI, we can write them as ordered pairs (x,y) and graph them on the coordinate plane. In this case, because the variables do not have any exponents greater than 1, all the ordered pairs will form a straight line. But that's not what this problem is asking for.
In this problem, they give you one part of an ordered pair ( ,18) and you have to find the other part of it. So we need to substitute 18 in for y, and then solve for x.
2x + 2/9(18) = 26
2x + 4 = 26
2x = 22
x = 11
Hope this helps!