standard_description: Use similar triangles to explain why the slope m is the same between any two distinct points on a non-vertical line in the coordinate plane; derive the equation y = mx for a line through the origin and the equation y = mx + b for a line intercepting the vertical axis at b.
problem_activity: Draw a tape diagram or balance for each equation or situation below.
a.   You purchase 4 gift cards, each in the same amount. You spend a total of $60.
b.
$${x+6=18}$$
c.
$${6x=18}$$


aligns: no