If you were to verbally repeat the argument in this ad to someone, you'd say something like, "We should fund the public schools so that they can buy new equipment for student athletes." Everyone would understand the reasoning.
However, if you wanted to restate the argument with an explicit 'because' (in order to make the reasoning super clear), you could say, "We should fund the public schools because they need money to buy new equipment for student athletes."
This is a proposal argument, because it's about taking a course of action.