It’s just adding the four areas (each is approximately the shape of a trapezium).
Total Area = 7.5x (8.8 + 7.1)/2 + 7.5x (7.1 + 9.8)/2 + 7.5x (9.8 + 8.5)2 + 7.5x (8.5 + 4.9)/2
= 7.5x [8.8 + 2(7.1) + 2(9.8) + 2(8.5) + 4.9]/2 = 242 m^2 (to nearest square metre)
The second equation line is in the format of the trapezoidal rule, whereby the heights (ie. y values of the function if this were a function graph) of all interval values are counted twice but the heights at the boundaries (ie. f(0) & f(n) if this were a function graph) is only counted once.