The cost, c, of a health club membership is related linearly to its length in months, m. if a 12-month membership costs $260 and an 18-month membership costs $380, which equation can be used to find the cost of a 30-month membership?

(12,260), (18,380)
slope(m) = (y2 - y1) / (x2 - x1)
slope(m) = (380 - 260) / (18 - 12) = 120/6 = 20

y = mx + b
slope(m) = 20
(12,260)...x = 12 and y = 260
now we sub
260 = 20(12) + b
260 = 240 + b
260 - 240 = b
20 = b

y = 20x + 20
c = 20m + 20now just sub in 30 for m and u will find c, the cost

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