A bank is comparing the quality of service given by its two most important branches. In branch A, 192 out of a random selection of 300 of its customers said that they were satisfied with the service. In branch B, 138 out of 250 randomly selected customers said that they were satisfied with the service. 

a. At the 5% level of significance, can we infer that branch A has a significantly higher proportion of satisfied customers than branch B? 

b. At the 5% level of significance, can we infer that the difference in the level of satisfaction with service between the two branches is wider than 5 p.c. points?  

c. Estimate with 90% confidence the difference in the level of satisfaction with service between the two branches.