Three pupils John, Daniel and David contributed a total of $400 for a party. John contributed $30 more than Daniel while, David contributed three times as much as John. If David contributed $x, which one of the equations below can be used to find David's contribution?

Daniel -- x

John --- x+30
David --- 3(x+30)

solve for x, the plug into my definitions

x + x+30 + 3(x+30) = 400

Let's break down the information given in the question:

1. John contributed $30 more than Daniel: Let's say Daniel's contribution is "y". Therefore, John's contribution is "y + $30".

2. David contributed three times as much as John: Let's say David's contribution is "x". Therefore, John's contribution is "1/3 * x".

Now, let's use these equations to find David's contribution.

According to the question, the three pupils contributed a total of $400. So, the equation becomes:

(y + $30) + y + x = $400

Simplifying this equation, we get:

2y + $30 + x = $400

Now, let's substitute the value of John's contribution (1/3 * x) into the equation:

2y + $30 + (1/3 * x) = $400

Since the question asks for the equation that can be used to find David's contribution, we can rewrite the equation as:

2y + (1/3 * x) = $400 - $30

Combining like terms, we can simplify the equation to:

2y + (1/3 * x) = $370

Therefore, the equation that can be used to find David's contribution is:

2y + (1/3 * x) = $370