Rodger's brother gave Rodger his collection of coins when he left for college. At that time, the value of the collection was $720. Twelve years later, the collection was worth $1080. What is the rate of change? Dong forget your units.

(0,720) (12,1080)

slope = (1080 - 720) / (12 - 0) = 360/12 = 30 < = = slope

y = mx + b

slope (m) = 30

(0,720) ... x = 0 and y = 720

sub and find b, the y int

720 = 30 (0) + b

720 = b < = = ur y int

ur equation : y = 30x + 720

ur slope is telling u that for every year, the value of ur coins goes up by 30 bucks

the y int is just telling u the original value

Slope = (1080 - 720) / (12 - 0) = 360/12 = 30 < = = slope

y = mx + b

slope (m) = 30

(0,720) ... x = 0 and y = 720

sub and find b, the y int

720 = 30 (0) + b

720 = b <==

equation : y = 30x + 720