Explanation
From the figure,
∠ XMN = ∠ XZY
Angle X is common
So, ∠ XNM = ∠ XYZ
Then from the angle relationship
XM/XZ = XN/XY = MN/ZY
XM = 8, XZ = 12 + 4 = 16,
XN = 12, XY = 8 + YM
8/16 = 12/(8+YM)
Cross multiply
8(8 + YM) = 192
64 + 8YM = 192
8YM = 128
YM = 128/8
= 16cm
From the figure,
∠ XMN = ∠ XZY
Angle X is common
So, ∠ XNM = ∠ XYZ
Then from the angle relationship
XM/XZ = XN/XY = MN/ZY
XM = 8, XZ = 12 + 4 = 16,
XN = 12, XY = 8 + YM
8/16 = 12/(8+YM)
Cross multiply
8(8 + YM) = 192
64 + 8YM = 192
8YM = 128
YM = 128/8
= 16cm