Q5. Fifteen kilometers a nice distance to ski in an afternoon.
O is
O are

Q6. Analysing sentences for grammatical purposes___
watching paint dry.
O is
O are
Q7. Economics___
almost as fascinating as accounting.

O is
O are

5. Fifteen kilometers is a nice distance to ski in an afternoon.

6.  Analyzing sentences for grammatical purposes is even better than watching paint dry.

7. Economics is almost as fascinating as accounting.

Explanation:

The use of "is" or "are" depends majorly on the condition of the noun involved. This means that if the noun is singular, we use "is" while for plural nouns, we use "are".

In the given sentences, "is" and "are" are used as follows-

5. In this sentence, the distance "fifteen kilometers" is taken as a single unit even though the word "kilometers" is in the plural state. Thus, the helping verb will be "is".

6. Here, the verb "analyzing" is taken as a gerund, thereby functioning as a noun. And so, the helping verb used will be "is".

7. Similarly, this sentence contains the noun "economics" which is a branch of study and thereby taken as a singular noun. Thus, the verb will be "is".

Thus, in all three sentences, the helping verb used will be "is".

the answer would be yes because the basket is full.