You write a check (#1121) to Martin's parents (Richard Smith) for February interest. Martin also asks you to include a $100 principal payment in the check. He wants to start paying his parents back. (TIP: Interest was paid through 1/31 on 2/1.) You write a check (#1121) to Martin's parents (Richard Smith) for February interest. Martin also asks you to include a $100 principal payment in the check. He wants to start paying his parents back. (TIP: Interest was paid through 1/31 on 2/1.)