Calculated field help

[kek979]

I am working on an assignment and I can't seem to get the calculated field right. I am to create a calculated field in the column after Amount that will figure taxes on purchases. Name the new field Taxes and multiply the Amount*7%. In the column next to Amount, I have entered Taxes:[purchases]*.07. It accepts the calculation, but when I try to see the new table, it says I must check the parameter. Will someone please help me?

[June7]

Is [purchases] the name of field in table? Maybe the expression should be:

Taxes: [Amount] * 0.07