7 lbs is 112 ounces. 112 plus 9 is 121. 121 plus 12 is 133. The total weight of the basket and the watermelon is 133 ounces. I'm not sure how you need the answer so I'll leave it in a couple different forms.
Ounces- 133
Pounds- 8.312 (rounds to the nearest tenth, 8.3)
Pounds and ounces- 8 pounds and 5 ounces