Respuesta :

(9,24)(12,32)
slope = (32 - 24) / (12 - 9) = 8/3

y = mx + b
slope(m) = 8/3
(9,24)....x = 9 and y = 24
24 = 8/3(9) + b
24 = 24 + b
24 - 24 = b
0 = b

equation is : y = 8/3x....when x = 21
y = 8/3(21) 
y = 168/3
y = 56 <===ur missing value is 56