(a) One of the 7 pictures is fixed; 6 other can be arranged in any order in the remaining 6 positions. The answer is 6! = 6*5*4*3*2*1 = 720 possible permutations. (b) 6! + 6! = 720 + 720 = 1440 possible permutations / arrangements. First 720 arrangements with the specified picture at the left end, and another 720 arrangements with the specified picture at the right end.