We know that the measure of the opposite angle and a side are related, so by determining which angle is bigger, we can discover which side is longer.
Angle SUD is greater than angle MUD. Angle SUD is the opposite angle to SD, and angle MUD is the opposite angle to DM. Therefore, SD is greater than DM.
You add the amount of pages that she has read in all which is 42+32=72. Then you subtract the sum by the amount fo pages in the book: 232-72 which equals 160
