Answer:It's not possible to earn an A in the courseI must have a 73 or MORE to earn a B in the courseStep-by-step explanation:The average obtained at the end of the course will be:[tex]\frac{85+78+84+x}{4} = av[/tex]Where x is the grade obtained in the final examination and av is the final average. To obtain an A, av has to be at least 90, av≥90, and to obtain an B, av has to be at least 80, av≥80Is an A in the course possible?So, if we get 100 on the final average:x = 100,av = (85+78+84+100)/4 = 86,75 and 86,75∠90.Answer: No, the higher grade obtained would be 86,75.What grade you must have in the final to earn a B in the courseTo earn a B, av≥80:[tex]av= \frac{85+78+84+x}{4 \ }\geq 80\\ \frac{247+x}{4}\geq80 \\247+x\geq 80*4\\ x\geq 320-247\\ x\geq 73[/tex]Answer: I must have a 73 or MORE to earn a B in the course