Subtract and use the least common multiple as the denominator for 2 9/10 - 1 7/ 18

Can someone me with this problem i don't understand i need

At the "no mutants allowed" country farm, every sheep has 4 legs, every chicken has two legs, and all animals have only 1 head. asked to count how many sheep and chicken are in the fields, a farm boy reports back that there are 140 feet and 50 heads. how many sheep and chicken are there? there are sheep and chicken at the farm.

Using inductive reasoning, what are the next two number in this set? 2,3/2,4/3,5/4,