As shown on the graph the 2 points mentioned have the following coordinates:
A(7,19) & B(11,11), That is A(x₁,y₁) & B(x₂,y₂)
the rate of change between A & B is the slope that is equal to:
slope = rate of change = (y₂-y₁) / (x₂-x₁) ==>(11-19) / (11-7) = (-8) / (4)
Rate of change = -2