The greatest common factor( GCF) of 36 and 84 is 12.
The easiest way for me to do this is too set their heights to actual numbers. Say Wanda is 100 feet tall (which I know isn’t a thing, but 100 is always an easy number for percentages.) If will is 34% taller than 100 feet, 1% is 1 foot, so Will is 134 feet tall. 134 / 100 is 134%, so will’s height is 134% of Wanda/s height. Hope this helps!