find the bounds first:
if all are oranges: number of oranges = $11.70/ $0.9 = 13
if all are pears : number of pears = $11.70/ $0.7= 16.71..
so the total number of fruits is between 13 and 16…
the total amount is $11.70 and cost of an orange = $0.90 and cost of a pear = $0.70, so the total number of fruits must be odd → 15
then you can use the supposition method / G&C method to find the number for each..