Question 413798
This effectively a set of simultaneous linear equations; if s is the number of scientific calculators and g is the number of graphing ones, you have been told that:
1) There are 50 calculators
--->   s + g = 50

2) The total cost was $1920
--->   s * 9 + g * 58 = 1920

We can solve these in the normal way:

*[invoke linear "s", "g", 1, 1, 50, 9, 58, 1920 ]

So the school ordered 20 scientific calculators and 30 graphical.