Ratio means to divide the number that comes first, by the number that comes next. So, you're dealing with a fraction. You see 14 girls first, so the top number (numerator) is 14. 21 boys is next, so that's the denominator. Now, the question asks...is that fraction equal to the other fraction they gave you...21 girls over 34 boys? That's what proportional means....equal. So, just make one fraction equal to the other, and cross multiply after simplifying both. If they total the same number, they're proportional.
Let's do it together: 14/21 does it equal 21/34? If you simplify 14/21 (divide by a common number that both can be divided by,) you will find out. Let's try using 7 to divide both the top and bottom of the first fraction. Will 7 go into both 14 and 21? Yes! How many times? 7 goes into 14 twice. So, the numerator is 2. 7 goes into 21 three times, so the denominator is 3. Our first fraction is 2/3. Now we just ask...does the first fraction equal the second fraction? 21/34? Let's see. First, let's simplify the second fraction. It looks like no number will go into both, evenly. Now, let's just cross multiply and see if the two numbers equal one another: Does 2/3 = 21/34. Cross multiply to find out (3 x 21) = (34 x 2) Solve and ask if the two numbers equal one another? 63 does not equal 68, so they do not equal one another, and therefore, they are not proportional.
Hope that helps you to understand.