13. 71.5=5.5u divide each side by 5.5 to solve for u
71.5/5.5=13 so u=13
14. 5/6x=5/14 to solve for x you divide both sides by 5/6. But to divide fractions you multiply the reciprical. So:
x=5/14*6/5=30/70 or 3/7
15. 44=t/11 multiply both sides by 11 to solve for t
484=t
16. 8.3=b/14 multiply both sides by 14 to solve for b
116.2=b
17. x/3= 15 multiply both sides by 3 to solve for x
x=45
18. 7.8x=23.4 divide both sides by 7.8 to solve for x
x=3