Me with number three explain your answer plz

What is f(3) for the quadratic function f(x)= 2x^2+ + x - 12

This is so harddd! solve. 1 + 1 = solve 4 + 4 = solve 3 x 3

Ricardo ran the 400 meter race 3 times his fastest time was 54.3 seconds his slowest time was 56.1 seconds if his average time was 55.0 seconds what was his time for the third race