Need help thanks

A technician compares repair costs for two types of microwave ovens (type I and type II). He believes that the repair cost for type I ovens is greater than the repair cost for type II ovens. A sample of 75 type I ovens has a mean repair cost of $77.53, with a standard deviation of $10.90. A sample of 66 type II ovens has a mean repair cost of $70.44 , with a standard deviation of $14.55. Conduct a hypothesis test of the technician's claim at the 0.05 level of significance. Let ul be the true mean repair cost for type I ovens and /2 be the true mean repair cost for type ll ovens. What is the standard deviation of the difference between the type I and type II repair costs? O 9.05 O 6.36 O 3.01 O 2.19