Jake's Roof Repair has provided the following data concerning its costs: For example, wages and salaries should be $21,000 plus $15.00 per repair-hour. The company expected to work 2,900 repair-hours in May, but actually worked 2,800 repair-hours. The company expects its sales to be $49.00 per repoir-hour. Required: Compute the company's activity variances for May. (Indicate the effect of each variance by selecting "F" for favorable, " U " for unfavorable, and "None" for no effect (i.e., zero variance). Input all amounts as positive values.)