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Given there are 12 inches in 1 foot, get rid of how many feet tall she is first. Olivia's 4 ft. 10 in., so we'll multiply 2.54 by 12 and then by 4. We get 121.92. Now we need to add in 10 more inches, so multiply 2.54 by 10, and we get 25.4. Add the two answers together to get Olivia's total height in cm, which is 
147.32 cm.
Now for Susan, who's 15 in shorter, we can find her height much easier. Multiply 15 by 2.54. We get 38.1, now we must subtract that from Olivia's total height to get Susan's total height, which will be 109.22 cm.
Hope this helps! Study hard.