This is in Calculus and its multiple choice only. Provide necessary solution for each items. Follow the numbering. Write the correct answer if not in the choices thank you and Godbless.

16. If the sum of two positive numbers is 8, what is the minimum sum of their cubes? A) 64 C) 128 B) 512 D) 256 18. What is the value of x on the function y = aresec(x) whose slope is 1? A) +1.732 C) +1.321 B) 11.272 D) 11.414