In each of Problems 18 through 22, (a) sketch the domain F over which the integration is performed; (b) write the equivalent iterated integral in the reverse order; (c) evaluate the integral obtained in (b). Describe Fusing set notation (in both orders). 18. dy dx 19. xydy dx V4-X' 1 20. (a' - yz)312 dy dx 21. 1 + x- dxdy 0 o 22. I + y' dy dx X