Thompson Instruments $($TI$)$ has proprietary technology and produces products for three market segments $$ commercial, defense, and international $($each segment is treated as a profit center$).$ After each segment produces its products, they are sent to a centralized TI testing lab for final testing and certification. The TI testing lab $($a cost center$)$ has the following cost structure: Fixed costs $$240,000($almost entirely depreciation$)$ and variable costs of $$30$ for testing hour. Outside testing can also be used to test TI products. Each outside testing firm can only test a particular TI product. The following table summarizes the prices charged by the outside testing vendors and the number of testing hours budgeted for each month for Year $1($assume that the amounts per month are constant across all months$).$ Commercial Defense International Budgeted testing hours per month $1,0002,0003,000$ TI has a policy of recharging the testing department$$s fixed and variable costs through a single overhead rate set at the beginning of the year based on the budget testing hours of all profit centers. Calculate the single overhead rate for testing. $$ a$.$ $$70$ b$.$ $$0$ c$.$ $$30$ d$.$ $$40$