Hi there! The fourth answer is correct.
In the picture we have to deal with facts:
1. The angle of 45°
2. The length of the opposite side
3. The length of the adjacent side.
Since we have to use the opposite and the adjacent side, we have to use the tangent of the angle. In a formula:

Filling in this formula, brings us to the following answer.
Answer:
$1200.
Step-by-step explanation:
We have been given that Kiersten runs a website that helps people learn programming. Every month, Kiersten receives a subscription fee of $10 from each of the subscribers to her website.
First of all we will find the number of subscribers for this month.


Now let us multiply number of total subscribers of this month by 10 to find the amount Kiersten will earn by her online business.


Therefore, Kiersten will earn $1200 this month by her online business.
(5x^3)(4x)^3
(5x^3)(2^2)^3 x^3
320x^6