If you add 690 ml of water you will obtain 1.690 liter of 70% alcohol. Of course if you halve the amounts, e.g. 0.5 liter 75% alcohol and 345 ml of water, you will also obtain 45% alcohol solution.
62 words per minute. You would divide 8 from 496 since you need to find out how many words he can type in a minute. Your answer is 62 words per minute.