Answer: the number of miles that Diane needs to drive for the two plans to cost the same is 100
Step-by-step explanation:
Let x represent the number of miles that Diane needs to drive for the two plans to cost the same.
The first plan has an initial fee of $57.96 and costs an additional $0.12 per mile driven. It means that the cost of driving x miles with this plan is
57.96 + 0.12x
The second plan has an initial fee of $61.96 and costs an additional $0.08 per mile driven. It means that the cost of driving x miles with this plan is
61.96 + 0.08x
For both plans to cost the same, the number of miles would be
57.96 + 0.12x = 61.96 + 0.08x
0.12x - 0.08x = 61.96 - 57.96
0.04x = 4
x = 4/0.04
x = 100 miles