The slope is 2.
Slope is a constant rate of change, and in this case, Jack is adding 2 to his original amount each month. This means the slope is positive 2.
BONUS: To explain the actual equation, y = mx + b, m is slope and b is the y intercept, or the starting point.
Since he already had five trains, the y intercept is 5.
Adding two trains each month is the slope, so m is 2.
The final equation is y = 2x + 5
