A manufacture of touch screens for tablets wants a MTBF of at least $50,000$ hours. Recent test results for $10$ units were one failure at $10,000hrs,$ one at $25,000hrs,$ and two more at $45,000$ hrs$.$ The remaining units were still running at $60,000$ hours.

a$)$ Percent of failures $=\%($enter your response as a percentage rounded to one decimal place$).$

b$)$ Number of failures $=$ failures per hour $($round your response to eight decimal places$).$

c$)$ MTBF at this time in testing $=$ hours $($round your response to the nearest whole number$).$