Ty received test grades of 83%, 74%, 77%, 77%, and 74%. a. what grade would he need to make on the sixth test to get a C if a C is at least 75% but less than 80%?

Im not sure what "what grade would he need..." means, so I am guessing you mean percentages. Just test each of the integer degrees from there and you will get the span of percentages that will work to get him a C.