if there are two numbers on one side, do i have to add them together?

Answer:
YES
Step-by-step explanation:
For example, in the figure displayed in the attachment, the length of [tex] YM = MS + SY [/tex]
[tex] MS = 3 [/tex]
[tex] SY = 10 [/tex]
Therefore, [tex] YM = 3 + 10 = 13 [/tex].
The lengths of segments MS and SY sums up to give you the length of YM.