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?

Answer 1

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

solve for x, the plug into my definitions

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