Answer: approximately 20.28051795
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Work Shown:
The given angles are A = 72 and C = 45. The missing angle B is
A+B+C = 180
B = 180-A-C
B = 180-72-45
B = 63
which is then used with this variation of the law of sines formula
sin(A)/a = sin(B)/b
sin(72)/x = sin(63)/19
19*sin(72) = x*sin(63) .... cross multiply
x*sin(63) = 19*sin(72)
x = 19*sin(72)/sin(63)
x = 20.28051795 approximately
Make sure your calculator is in degree mode.