The creation of the path 5m wide around the perimeter would add 10 m to the total length and 10 m to the total width. (assuming the the edges are squared off). The total area
would be 100m by 85m or 8500 m^2.
Subtracting the park size itself 90m by 75m or 6750m^2 from the total reveals the path size to be 1750m^2.
Alternatively, this could be figured by multiplying 5 meters by the perimeter 330m plus the corners 4 * 5^2 = 1750m^2.
Some people will argue the the corners should be rounded. This would make each corner a quarter circle. Together, all four corners would make a full circle with a radius of 5.
The would make the total area of the corners 25*pi for a total area of approx. 78.54m
so, for squared corners, the area of the path is 1750m^2
and for rounded corners, the area is 1728.54m^2.
I came up with 1650m.
l*w for each segment of the path.
The path's width is 5m.
2(5*75)+2(5*90) = 1650 meters squared
Then you have to take into account that there is an overlap and you'll have to add 10 extra meters to either the length or the width -- your choice (5 on each side) making an extra 100 meters squared.
area of the park with path is (90 + 10)(75 + 10)
= 100 x 85
= 8500 sqm
area of the park without path is 90 x 75
= 6750 sqm
the difference in the two areas is
= 8500 - 6750
= 1750 sqm