(4x - 1)(3x + 5)
Try different combinations of the front number's factors with combinations of the last number's factors. The FOIL until you find one that works.
Average age of the 4 tigers is 17
add all the ages 22,13,18,16 and divide by
Well, for 20 you just add them, to get

. For 21, you do a substraction:

. It'd take him quite some time (does this one even have zeros? :)) )