Sally paid $3.50 for 7 apples.

each apple costs 50 cents

Step-by-step explanation:

3.50/7=0.50

the height of the surface increases from the center out to the sides of the road.

step-by-step explanation:

as we move out we move away from the x-axis.

and as mentioned in the problem statement that height of a road increases when we move away from the center x.

hence proved that 3rd option

the height of the surface increases from the center out to the sides of the road.

is the correct option.