Number of test-cases for a boolean function

I'm confused about the number of test cases used for a boolean function. Say I'm writing a function to check whether the sale price of something is over $60 dollars.

function checkSalePrice(price) {
  return (price > 60)
}

In my Advance Placement course, they ask the minimum # of test include boundary values. So in this case, the an example set of tests are [30, 60, 90]. This course I'm taking says to only test two values, lower and higher, eg (30, 90)

Which is correct? (I know this is pondering the depth of a cup of water, but I'd like to get a few more samples as I'm new to programming)