Answer:
90 calories in a banana.
Step-by-step explanation:
O = B - 20 where O is the number calories in an orange and B is a that in banana.
Also 7B = 9O
From the above O = 7B / 9 so substituting in the first equation:
7B / 9 = B - 20
7B = 9B - 180
2B = 180
B = 90.
