See the Math Notes box in Lesson 4.1.4 for a review of intervals and scaling.
Remember that where the x- and y-axes intersect is always 0. To scale the x-axis in part (a), you should try dividing 12 by 3, since that is the number of spaces between 0 and 12.
The x-axes for parts (a) and (b) are labeled below. Were you able to scale the y-axes?