Arectangular park is 150 yards on one side and 125 yards on the other.
a. if debbie walks around the park 2 times, how far does she walk ?
b. if debbie wanted to walk 1,000,000 yards, how many times would she have to walk around the park ?

So, there is a rectangular park with longer side (length) 150 yards and shorter side (width) 125 yards.

so walking around the rectangular park once is like covering the Perimeter (p) of the rectangular park.

So, lets find the perimeter of the park.
Perimeter of rectangle = 2 ( l + w)
                                    = 2 ( 150 + 125 )
                                    = 2 * 275
                                    = 550 yards

Now, walking around the park two times is like doubling the Perimeter of the rectangle. So, when Debbie walks around the park 2 times, he covers the perimeter of the rectangular field twice.

i.e. Debbie walked 2 * Perimeter
                               = 2 * 550
                               = 1100 yards

Now, If Debbie wanted to walk 1,000,000 yards, she has to walk the  rectangular park (1,000,000 / the Perimeter of the park)
         i.e.  1,000,000 / 550
             = 1818.18 times

So, 
(a) she walks 1100 yards
(b) She have to walk 1818.18 times