Dai is comparing how many trading cards he has with his friend Maura. Initially, they find out that Dai has 4 more cards than twice the number Maura has. If there are 25 cards all together, how many does each person have?

List x1, x2, x3, x4 where xi is the left endpoint of the four equal intervals used to estimate the area under the curve of f(x) between x = 4 and x = 6. a 4, 4.5, 5, 5.5 b 4.5, 5, 5.5, 6 c 4.25, 4.75, 5.25, 5.75 d 4, 4.2, 5.4, 6