Nicholas bought 5 pens for $3 at this rate how much will he spend on 10 pens?

Okay so, let's analyze the question first.

We're looking for the cost of the 10 pens that Nicholas bought, right? If he bought 5 for $3, how much do you think the 10 pens will cost?

If you multiply 3 by 2, because he'll buy twice as much as he bought the first time, it'll equal 6.

So..

5 pens = $3
10 pens = $6

If he buys 15, 20, or 25 pens, it'll equal..

5 pens = $3
10 pens = $6
15 pens = $9
20 pens = $12
25 pens = $15

We're basically counting off by 3 to know the cost. I hope this helps!