Daniel had 288 more than Edwin. After Daniel spent 1/6 of his money and Edwin spend 3/4 of his money, Daniel had $303 more than Edwin. How much did Daniel have at first?

Just translate all that verbiage into Math

Ed --- x
Dan ---- x+288

after the spending:
Dan had (5/6)(x+288) = 5x/6 + 240
Ed had (1/4)(x) = x/4

(5x/6 + 240) - x/4 = 303
times 12, the LCD
10x - 3x + 2880 = 3636
7x = 756
x = 108

check:
Ed had 108
Dan had 108+288 = 396

Ed spent 3/4 of his, leaving him with 1/4(108) = 27
Dan spent 1/6 of his , leaving him with (5/6)(396) = 330
Does Dan have 303 more than Ed ??? YES, 330-27 = 303