Think about it like this:
At 100C, water boils. At 0 C, water freezes. 100 - 0 = 100
At 212 F, water boils. At 32 F, water freezes. 212 - 32 = 180
Therefore, each C degree is = to 180/100, or 9/5 of an F degree.
At 373 K, water boils. At 273 K, water freezes.
Therefore, K - 273 = C, and C + 273 = K
Also, (100C x 9/5) + 32 = F
Suggestion: draw three thermometers vertically and side by side. Label one K, one C, and one F. Place the respective temperatures of freezing and boiling water on each at the same horizontal level.