Answer: he ate 12 cookies
Explanation:
Let x represent the number of cookies that Landon ate last week.
Let y represent the number of cupcakes that Landon ate last week.
Last week , Landon ate a total of 19 cookies and cupcakes. This means that
x + y = 19
If the cookies contain 140 calories each the cupcakes contain 275 calories each, and he consumed a total of 3605 calories, it means that
140x + 275y = 3605 - - - - - - - - - -1
Substituting x = 19 - y into equation 1, it becomes
140(19 - y) + 275y = 3605
2660 - 140y + 275y = 3605
- 140y + 275y = 3605 - 2660
135y = 945
y = 945/135 = 7
x = 19 - y
x = 19 - 7 = 12