Find the first partial derivatives of the function. (sn = x1 + 2x2 + ... + nxn; i = 1, ..., n. give your answer only in terms of sn and i.) u = sin(x1 + 2x2 + ⋯ + nxn)

On a farm, the ratio of the number of old sheep to young sheep to little sheep is 3: 13: 4. there are 600 sheep in total. each old sheep consumes 4.5 pounds of grass per day and each little one consumes 2 pounds of grass each day. if the sheep on the farm, altogether, eat 3765 pounds of grass each day, how much grass does a young sheep consume per day, in pounds?