The problem consists in comparing a pair of numbers, one in fraction form.
So there will be enough room for the piano if 5 feet is greater than 19/4 feet. Lets transform the numbers so is easier to compare:
5 = 5/1 = 20/4
Now we can compare easily:
20/4 > 19/4
that is because fractions can be compared directly if their denominator is equal (the lower part of the fraction)
or
5 > 19/4
that is because 5 = 19/4
so there is plenty of room for the piano in the room
In a number line, we have
19/4 ------------- 20/4
that is, 19/4 is at the left of 20/4