You can’t “solve” a single equation containing two variables. You would need at least two equations to do this. But the equation can be simplified by dividing each term by 100:
X+3Y=200.
As it stands, the equation represents a relationship between X and Y and this relation can be represented by a straight line graph, so that every point on the line represents a solution (one of an infinite number) to the equation. To draw such a line, mark the intercepts (x intercept=200, y intercept=200/3) and draw a line to pass through the intercepts.