Question for algebra people?

Question

Anyone who can help me understand why this is the answer?

A blend of coffe is made by mixing Comombian coffee at $8 a pound with espresso coffe at $3 a pound. If the blend is worth $5 a pound, how many pounds of the Colombian coffe are neeeded to make 50 pounds of the blend?

Answer is 20

Answer 1

50 pounds of the blend are made of X pounds of the colombian coffee and 50-X pounds of the espresso coffee, and are worth 50*5$ = 250$.

You should find 250$ by calculating the sum of the cost of the two types of coffee, which is:

8*X+3*(50-X)=250 -->5*X+150=250

thus: X=100/5=20.

Answer 2

8x + 3y = 250

x + y = 50

y = 50 - x

substitute 50 - x for y in the top equation and you have

8x + 3(50-x) = 250

8x + 150 - 3x = 250

5x = 100

x = 20