Simplified the answer is in decimal form 0.00000026.
81,85,89 are the missing numbers
1/2 + 1/2 =1 cup + 1/2 + 1/2= 2 cups + 1/2= 2 1/2
How many 1/2 you see? 5!!
30b + 100u = 900
5b + 25u = 200....multiply by -6
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30b + 100u = 900
-30b - 150u = - 1200 (result of multiplying by -6)
------------------add
-50u = - 300
u = 6 <== upgrated phones sold
30b + 100u = 900
30b + 100(6) = 900
30b + 600 = 900
30b = 900 - 600
30b = 300
b = 10 <== basic phones sold
