You can put this solution on YOUR website! Assuming the 4 and 2 are exponents,
Sub x for m^2
(x+16)(x-3) = 0
x = 3, -16
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Sub back
m = ± sqrt(3)
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m = ± 4i
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You might factor that, too.
Same answers, simpler, but if factoring isn't possible, substitution always works.