Your mother asked you to turn the oven down to 325 degrees Fahrenheit This is 75 degrees fahrenheit less than it was. What was the original temperature

The original temperature was 400 degrees.

You turned down the oven to 325 degrees, it was 75 degrees less that it originally was. This means you subtracted 75 degrees from 325 degrees and to find the original number, you have to add the 75 degrees back.

325 + 75 = 400

Say a cookie jar has 35 cookies. It's 7 cookies less than it originally was. You would get in trouble if your mother discovers 7 cookies are missing. So, you have to replace the 7 missing cookies with other cookies that you found in the house. How many cookies are you replacing?

The jar had 35 cookies, but you replaced the missing 7. In other words, you added 7 to 35. Now, all the cookies are at the original amount of 42.