text: Wow, you really messed up typing. Might try the space bar next time. :-D\n\nAnyway, I think you're asking, "Find out the [longitude] of a place Q where [the] local time is 10:30 AM, while the local time of another place P, situated at 40 degrees [longitude], is 2 PM."\n\nSo you know that the earth has 360 degrees of longitude (you go the whole way around and you cover a circle). You also know that if you go the whole way around the world, you'll pass through every time. So you have 24 hours.\n\nProportion: 24 hours = 360 degrees\n\nThe difference between the two times (10:30 AM and 2 PM) is 3 hours and 30 minutes, or 3.5 hours.\n\nProportion: 3.5 hours = ? degrees\n\n24 / 3.5 = 360 / x\nCross-multiply:\n24 * x = 3.5 * 360\nx = 3.5 * 360 / 24 = 52.5\n\nProportion: 3.5 hours = 52.5 degrees\n\nSo we know that the change in longitude is 52.5 degrees. Now the question is whether to add or subtract that from 40 degrees, which we know is the original (P). From P to Q, we're going backwards in time, which we know is westwards (look at time zones, or think about TV ads that say that a show is airing at 8 eastern, 7 central). So we need to move 52.5 degrees west. If your 40 degrees is already 40 W, then add +52.5 W to get 92.5 W. But if it's 40 E, then you need to move in the opposite direction. 40 - 52.5 = -12.5 E, or 12.5 W.