You are given the height of the building and the length of the shadow the building gives, so you can set that up as a proportion of Height of building over the length of the shadow so 31/28.
Now you can set the same proportion for Julian, using X for her height, so you would have x/6.
To solve for her height, set the two proportions equal and solve for x:
31/28 = x/6
Cross multiply:
31 * 6 = 28 *x
186 = 28x
Divide both sides by 28:
x = 186 / 28
x = 6.64 feet tall
