pls let me know how to do this.

18. Use the properties of the derivative to find D,[r(t) . u(t)] given the following vector-valued functions. r(t) = 2ti + 3+3j+ 5+3k u(t) = 4i + 5t2j - 473k19. Find the open interval on which the curve given by the vector-valued function r(0) = (60 + 6sino)i + (10- 6cos@)j is smooth.20. Find r(t) given the following. r'(t) = 20t j + 10tak, r(0) =-5i + 20j 21. Use the properties of the derivative to find D,[r(t) X u(t)] given the following vector-valued functions. r(t) = 5ti -2t'j + 412k u(t) = 4i + 212j + 3+3k 22. Find r'(t) - r" (t) given the following vector function. r(t) = (412 + 4t)i + (312 + 3t)i