pls help answer these

RULES AND PROPERTIES OF WORK: If two entities are working on the same job, and the first would take a hours to complete the job alone and the second b hours to complete the job alone, then the equations =+ = = =, can be used to find t, the time it will take to complete the job together. 23. Sully can grade a class set of Back 2 Basics in b minutes. Brust, who's a bit slow, takes 12 more minutes than Sully to grade the same class set. Together they can grade them in 8 minutes. How long does it take for each of them to grade them by themselves? Sully: Brust: 24. Rationalizing the numerator a. What is the excluded value for the rational function, f (x) = Vx-4, x - 16 b. Rationalize by multiplying by the conjugate of the numerator. c. What value does the function now approach, as x approaches the excluded value you found in part A? 25. FINDING THE DERIVATIVE. In Calculus the definition of a derivative is f'(x) = lim /(xth)-j@ Let f (x) = 2x2 -5x. a. Plug f(x) and f (x + h) into the derivative formula and simplify. b. Reduce your simplified function by factoring out a common factor of h. What is the derivative of f (x)