Find each worker`s rate per minute, add them, then take the reciprocal for the combined time.<br><br>
&bull; X`s rate = \( \frac{1}{19} \), Y`s rate = \( \frac{1}{12} \), Z`s rate = \( \frac{1}{12} \) field per minute.<br>
&bull; Combined rate = \( \frac{1}{19} + \frac{1}{12} + \frac{1}{12} = \frac{1}{19} + \frac{2}{12} = \frac{1}{19} + \frac{1}{6} \)<br>
&bull; \( \frac{1}{19} + \frac{1}{6} = \frac{6}{114} + \frac{19}{114} = \frac{25}{114} \) field per minute<br>
&bull; Time = \( 1 \div \frac{25}{114} = \frac{114}{25} = 4\frac{14}{25} \) minutes<br><br>
Check: In \( \frac{114}{25} \) min, X does \( \frac{114}{25 \times 19} = \frac{6}{25} \), Y does \( \frac{114}{25 \times 12} = \frac{19}{50} \), Z does \( \frac{19}{50} \). Total = \( \frac{6}{25} + \frac{19}{50} + \frac{19}{50} = \frac{12+19+19}{50} = \frac{50}{50} = 1 \). ✓<br><br>
Final Answer: A = 4, B = 14, C = 25