4 Tbsp. = 1/4 cup. Burn that into your brain, as it's one of the more useful conversions for the home cook.
The recipe for the peanut marinade calls for 4 Tbsp. soy sauce, 2 Tbsp. red wine vinegar, and 6 Tbsp. peanut butter. So pull out the measuring cup, add 1/4 cup soy sauce, 1/8 cup vinegar (now a total of 3/8 cup), and then add enough peanut butter to bring the liquid level up another 6 Tbsp. (3/8 cup), now for a total of 3/4 cup. Have you ever tried measuring 6 Tbsp. of peanut butter using measuring spoons?