tariff = (export - import) / (<??? factor> × <another ??? factor that cancels the first one out> × import)

The only times anyone would use the asterisk as multiplication symbol are

• they are doing some fancy math and it’s not the same kind of number multiplication we’re familiar with
• they are on a computer, the keyboard does not have a (×) key, and they don’t know how to typeset it (\times in LaTex), so they just use the asterisk instead

The US government falls in the second category.