<PRE><B>Question 33143</B>
FIRST form equations with the informations given in the question.
  
  let O be the calories of orange and B be the calories of Banana.

eq 1. O = B - 20

eq 2. 7*B = 9* O
 put the value of O from eq 1. in eq 2.,
  we get,

 7*B = 9*( B- 20)

  7B = 9B - 180

  REARRANGE THE VARIABLE ON ONE SIDE AND NUMBER ON THE OTHER SIDE.
we get,

 180 = 9B -7B

  180 = 2B
therefore B = 180/2
            = 90 CALORIES IS THE ANSWER.

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