There are multiple ways to go about solving this problem (solving by calculating the areas of the individual, smaller shapes), but I recommend solving it by first calculating the area of the entire figure (96 units - 12 * 8 - length * width ((formula for the area of a rectangle)) and then subtracting the area of the missing part from this value.
Assume the opposite sides are equal in value (see picture for work) and subtract the given values (4 and 5) from 8 and 12 to get the measurements to find the triangle (the missing part).
You get 7 and 4 and now you use the formula for the area of a triangle to get the area. (7*4)/2, which gives you 14 units.
Subtract 14 (area of missing value) from 96 (area of total value) to get your final answer, 82 units!
