Identify the population and sample: a survey of 1353 American households found that 18% of the households own a computer.

Given:
Protein smoothie costs $10
Berry smoothie costs $6
Total smoothies sold  = 100
Total money collected = $836

Let
x = number of protein smoothies sold
y = number of berry smoothies sold

Then
x + y = 100           (1)
10x + 6y = 836     (2)

From (1), obtain
y = 100 - x            (3)

Substitute (3) into (2).
10x + 6(100 - x) = 836
4x + 600 = 836
4x = 236
x = 59
y = 100 - x = 41

59 protein smoothies and 41  berry smoothies were sold.