Solution :
[tex]U(A, B) = 5A + 2B[/tex]
a). Bundles [tex](40, 5)[/tex] = U ( _____ , 2), lie on the same indifference curve. Suppose missing numbers is x.
So, [tex]U(40, 5) = U(x, 2)[/tex]
  (40 x 5) + (2 x 5) = 50x + (2 x 2)
   210 - 4  = 5x
    [tex]x = 41.2[/tex]
So Alexander has [tex]40[/tex] apples and [tex]5[/tex] bananas. The indifference curve though [tex](40, 5)[/tex] also include bundle.
Therefore, (41.2, 2)
b). [tex]$MRS_{BA} = \frac{MU_B}{MU_A}$[/tex]
         [tex]$=\frac{\delta U/\delta B}{\delta U/\delta A}$[/tex]
         [tex]$=\frac{2}{5}$[/tex]
         = 0.4
So Alexander  has [tex]40[/tex] apples and [tex]5[/tex] bananas with this bundle. Alexander would like to give up [tex]0.4[/tex] unit apples for a banana.