Lets say Ben and Jerry sold 'x' number of shakes.
If they have sold 'x' number of shakes then they must have sold
number of cones.
Now, each ice cream cone costs $2.00 and each shake costs $9.00.
Last month the total sale totaled $3,900.00
Now,
The equation to represent the relation between the total sales and number of ice cream cons, number of shakes sold is given by:



Solving for 'x' we get:

We had assumed that 'x' number of shakes were sold, therefore we know that 300 shakes were sold and
numbers of cones were sold which means
ice cream cones were sold.
So, 600 ice cream cones were sold and 300 shakes were sold last month.