This is an linear equation, so
y=mx + b
m= money w=weeks
m= -20w +200
You're very close. However, the less steep line should go through (4,7) and not some point slightly above that location. Also, the shaded region should be above both dashed lines at the same time. So you won't include the portion that I've marked in blue (see attached). Other than that, it looks great.
1% of 19,500= 195
6% = 1%x6 = 195x6 = 1170
19500+1170=20670
8/9 - 1/5
= 5(8/9)-9(1/5)
=(40/45)-(9/45)
=31/45
therefore 31/45 of the estate would go to the American cancer society