9/100 = x/90
Cross multiply to get 810 = 100x
Divide both sides by 100 to get x = 81 inches
B is the best strategy. (You mentioned an option D, but it's not shown in your question!!)
This problem boils down to 5/6 - 1/4
To subtract these fractions you need a common denominator.
I'll use 12
The first fraction becomes 10/12 and the second fraction becomes 3/12
10/12-3/12 = 7/12
So Jacob is 7/12 of a foot taller than Linda.
Also note than since 12 inches = 1 foot, you could say Jacob is 7 inches taller than Linda
1.11 2.14 3.10 4.9 5.-5 6.-8 7.11 8.40 9.9 10.12 11.30 12.22 13.3 14.-4 15.16 16.35