The weight of Jacob's backpack is made up of the weight of the contents of the backpack as well as the weight of the backpack itself. Seventy percent of the total weight is textbooks. His notebooks weigh a total of 4 pounds, and the backpack itself weighs 2 pounds. If the backpack contains only textbooks and notebooks, which equation can be used to determine t, the weight of the textbooks?

0.7 (t) = t - 4 - 2

0.7 (t) = t + 4 + 2

0.7t (4 + 2) = t

0.7 (t + 4 + 2) = t