Notice those two points on the "linear graph", the first point is at (1965 , 140) and the second point is at (1990 , 100).
the rate or average rate of change, namely the slope will then be
9*(5-y)
nine times is 9* and the difference of 5 and y is 5-y
You can factor out a GCF of 7 out of all of the terms. The answer would be 7(3a+4b).