Henry knows that whenever he buys something, he is charged a sales tax. This sales tax (t) varies directly with the amount of money (m) he spends. Write an equation representing the direct proportional relationship between the sales tax and the amount of money spent. Use the variable k as the constant of proportionality.
If Henry pays $1.76 in sales tax on an item that costs $22, what is the value of the constant of proportionality?
What does the constant of proportionality represent in this problem?