Determine the interest on the following notes: (Round intermediate calculations and answers to 2 decimal places, eg. 52.75.) (a) $2,000 at 6% for 90 days. (b) $900 at 9% for 5 months. (c) $3,000 at 8% for 60 days. (d) $1,600 at 7% for 6 months. \$