Proportional linear relationships can be used to solve problems by using the slope-intercept form of a linear equation. This form of equation can be used to determine the relationship between two variables, and can be used to solve for one variable when the other is known.
Nonproportional linear relationships can be used to solve problems by using the point-slope form of a linear equation. This form of equation can be used to determine the relationship between two variables, and can be used to solve for one variable when the other is known. Additionally, this form of equation can be used to determine the equation of a line when two points on the line are known.