56=1/2(b)(7)

56=1/2 b  7        Multiply both sides by 2

112 = b7          divide by 7

b = 16

56=1/2(b)(7)

The equation is not defined unambiguously.
Use math brackets.

56=(1/2)(b)(7)    \(\large 56=\frac{1}{2}\times b\times 7\)     \(b=\frac{56\times 2}{7}=16\)

or

56=1/(2*b*7)       \(\large 56=\frac{1}{2\times b\times 7}\)     \(b=\frac{1}{56\times 2\times 7}=1.27551\times 10^{-3}\)

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