The first part is 1325
10 x 35=350
15 x 65=975
The you add them which equals 1325
To find the area of an obtuse triangle you have to multiply the base of the triangle by the vertical height and divide the result by 2 following the formula:

The base of the triangle is b= 7 miles and the height is h= 8 miles, using these lengths calculate the area as follows:

The area of the triangle is 28 square miles.
I think the percent change would be 25%