What is worth more? $$100$ today or $$100$ a year from now?

If you want $$180,000$ in $3$ years at $8\%$ how much do you need to set aside today?

If you set aside $$500$ today and get $$800$ a year from now, what is your interest rate?

Your goal is to save $$10,000$ for a down payment on a house in $4$ years. You find an investment that pays $6\%$ interest. How much do you need $t$ invest today to reach your goal of $$10,000?$

You have a $$500$ tax refund and you invest that in an investment paying $5\%$ annually. How much will that be worth in $5$ years?