Need ! multiple questions [lots of points] ! show work

What's the difference between: x≥0 and nonnegative integer. ?

Two blends of tea are mixed to make a blend that will be sold at the fair. black tea sells for $2.20 per pound and orange pekoe tea sells for $3.00 per pound. how much of each should be used to obtain a 4lb blend selling for $2.50 per pound?

Divide: 1573 ÷ 7 = a) 222 r5 b) 223 r6 c) 224 r5 d) 224 r3