Using the Law of cosines we have:

b^2 = a^2 + c^2 - 2ac cos(87)

b^2 = 8.75^2 + 4.26^2 - 2*8.75*4.26*cos(87)

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click here to see the step by step calculation for b

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b = 9.53 cm

We need to ignore the negative solution since the length of the side can not be negative.

The length of the side b is 9.53 cm.