Let x be the amount, in pounds, of the sumatra coffee. With this representation, the amount of Colombian coffee may be represented as 50-x. The equation that would allow us to solve for the value of x is the price balance of the given coffees.
2.5x + (3.75)(50 - x) = (50)(3.35)
The value of x from the equation is 16.
Therefore, he needs 16 lbs of sumatra coffee and 34 lbs of Colombian coffee.