Hi there!
Let's solve this problem step by step!
A bottle contains 70% alcohol. First we need to convert this percentage into a decimal. To do this, we only need to divide by 100.
70 % = 70 / 100 = 0.7
The entire bottle contains 500 ml of solution. To find the amount of alcohol in the solution, we must multiply our (just found) decimal by the total content of the bottle.
0.7 * 500 ml = 350 ml
Therefore there are 350 millimetres of alcohol in the solution.
~ Hope this helps you!