Answer: 6 pounds of Kona blend are needed in order for you to prepare the same secret blend.
Step-by-step explanation: When mixing 70 pounds of Terraza blend, you have to use 21 pounds of Kona blend. If one day you only have 20 pounds of Terraza blend, x will be the weight you would have to mix in order for you to prepare the secret blend. Using cross multiplication, our calculations will look like this:
70 pounds Terraza - 21 pounds Kona
20 pounds Terraza - x pounds Kona
70x = 21.20
70x = 420
x = 420/70
x = 6 pounds of Kona blend to 20 pounds of Terraza blend.