Let's assume that the cost of an eraser is x dollars. Then, according to the problem, the cost of a pen is 6 times the cost of an eraser, or 6x dollars.

We know that Raj bought 5 pens and 19 erasers, so we can set up an equation to represent the total cost of his purchases:

5(6x) + 19x = 83.30

Simplifying this equation, we get:

30x + 19x = 83.30

49x = 83.30

x = 1.70

Therefore, the cost of an eraser is $1.70. To find the cost of a pen, we can substitute this value back into our expression for the cost of a pen:

6x = 6(1.70) = 10.20