Answer:
114 watches
Step-by-step explanation:
1. Create an x and y graph. The first x as 25 watches and y as $100 since 25 watches cost $100. Also, in the y column just add $50 in parenthesis next to the y's so you know that each time Sarah gets an additional bonus. Then continue the pattern, with the x column adding by 25. You should stop once you reach 100 watches.
It should look like...
x y
25w $100 ($50)
50w $200 ($50)
75w $300 ($50)
100w $400 ($50)
2. Now you know that 100 watches with additional bonuses cost $450, you create the expression, 450+4x=506 to find out how many watches more need to be sold so the total is $506.
3. Subtract 450 from both sides so the expression simplifies to 4x=56. Then divide 4 on both sides, which gives you 14.
4. Now add the original amount of watches that made 450, which was 100 with 14. This gives you 114 watches.