Excel question! Need help with payroll unemployment formula?

The taxable earnings for unemployment is based on the first $7000. The Beginning ulative Earning was $6430, after the week's pay of $943, the Ending ulative Earnings was $7373. Which means of the $943 gross pay, only $570 should be subject to the tax. I know how to do it by hand, but I'm not very good on Excel and my teacher wants me to do everything in formulas but I cant figure this one out! could anyone please help!