#8) Subtract 350 from each side then divide each side by 25 to get (c-350)/25 = h.
Plug in 950 for c to get (950-350)/25 = h.
600/25 = h = 24 hours.
#9 is the same as number 8 just with one more variable. Subtract 2.25h from both sides and divide both sides by 1.75. Then plug in 18.25 for t and 5 for h. Then solve for d.