Matlab help with array and writing a program?

Can anyone please explain to me how to use mat lab to write a program that computes the array B by computing the natural log of all the elements of A whose value is no less than 1 and adding 20 to each element that is equal to or greater than 1. Use a for loop with conditional statements. A=[ 3, 5, -4; -8,-1, 33; -17, 6, -9] PLEASE AND THANK YOU!