Does it equal 7,140 and did i stack it right

Correct. 357 × 20 = 7,140 (Just make sure the 20 × 7 column is 140, not 14).

Checking this:

7,140 ÷ 20 = 357

Hope this helps!

Yes it does equal 7,140, and make sure the last column is 140 not 14.
Hope this helped, and Good Luck! :D

The length of what is left would be 1 1/2 feet long.

Okay so for every triangle has three angles that always add up to 180 degrees. and to tell the difference between whether they are secure, right or obtuse is that acute: has one angle that is less than 90 degrees. right triangle means there is at least one angle that is exactly 90 degrees. and an obtuse angle has an angle that is bigger than 180 degrees. i’ll do #13 as an example: 13. 40 and 50 so if every triangle has 180 degrees 40+50= 90 degrees then180-90= 90 degrees so the third angle is 90 degrees and because this triangle has a 90 degree angle it means it is a right triangle