I’m so sorry I really don’t know the answer but try the internet
Please see pic, I'd solved in it.
One decimeter equals 10 centimeters. So 3 decimeters equals 30 centimeters. They are equal.
You just take the difference between them and the answer is 1 3/5
A multiplicative inverse of an integer a is an integer x such that the product ax is congruent to 1 with respect to the modulus m.
1. 
Check:
The multiplicative inverse of 5 in
is 9.
2. 
Check:
The multiplicative inverse of 5 in
is 5.
3. 
Check:
The multiplicative inverse of 5 in
is 8.