The figure on the top left is a triangle with base 11 and height 8, for an area of

Immediately below, we have a rectangle with dimensions 11 and 9, for an area of

Moving to the right, we have a parallelogram with base 9 and heght 11, which again has height

Finally, the rightmost figure is a triangle with base 8 and height 9, for a total of

Sum these areas and you'll get the total area
Let the number of hours be x.
70 + 80x < 100x
20x > 70
x > 3.5