Write a function in python named exes that uses the function letterX to draw a sequence of X's of specified size and separation. The midpoints of the X's all lie on a line. The function exes takes 5 parameters: 1) t, a turtle 2) initSize, the length of the lines in the first X 3) deltaSize, a floating point number between 0 and 1 that is the ratio of the length of the lines of successive X's 4) separation, the distance between midpoints of successive X's 5) xNum, the number of X's to draw