Give one example od when you would use the friendly numbers estrategy to subtract

Friendly number. An addition/subtraction strategy that uses a number that is easy to work from, typically 10 or a multiple of 10. For example, to solve 16 – 9, one might recognize that the friendly number 10 is 6 less than 16, then count down 1 more to 9 to find that the difference is 7.

For range i think it’s area