Atree casts a shadow that is 8 feet long, a 3 foot mailbox cast a shadow that is 5 feet long. how tall is the tree?

Set up two fractions:
8/x and 3/5
Set them equal to each other and cross multiply to get:
8*5 = 3x
40 = 3x
13.3 = x or 13 and 1/3 feet tall. 

Abit confused about what you mean, but i think you might be referring to slope intercept form: y = mx + bin that case b, or the y intercept is already given.(0,-1)find the slope by using the formulay2 - y1/x2 - x1the final slope will be 4/2, equivalent to 2.now your equation should look like thisy = 4/2x -1sorry if this didn’t you out!