Bob has some 10 lb weights and some 3 lb weights. Together, all his weights adds up too 50lbs. If x represents the number of 3lbs and y represents the number of 10 lbs, which equation can be used to find te number of each type of weight bob has? A: 3x-10y=50 B: 3x=50-10y C: 50+10y=3y or D: 50+3y=10y