At 1pm the shadow of a tree is 14 ft long. at the same time the shadow of a telephone pole is 21 feet long. what is the height of the tree

Part A: two expressions equivalent to 3(m + 5 + 9m) are 3(5 + 10m) and (3m + 15 + 27m)

Part B: 3(m + 5 + 9m) = 3(5 +  m + 9m) = 3(5 + 10m)    [associative property]
3(m + 5 + 9m) = (3m + 15 + 27m)    [distributive property]

Part C: Let m = 2: 3(m + 5 + 9m) = 3(2 + 5 + 9(2)) = 3(7 + 18) = 3(25) = 75
3(5 + 10m) = 3(5 + 10(2)) = 3(5 + 20) = 3(25) = 75
3m + 15 + 27m = 3(2) + 15 + 27(2) = 6 + 15 + 54 = 75