Step 1: Understanding the Concept
The joint equation of two lines is the product of their equations set equal to zero.
Step 2: Key Formula or Approach
Line 1: parallel to X-axis through \((1,4)\), so \(y-4=0\). Line 2: slope \(\tan45^{\circ}=1\) through \((1,4)\), so \(y-4=x-1\), i.e. \(x-y+3=0\).
Step 3: Detailed Explanation
\[ (y-4)(x-y+3)=0 \]
\[ xy-y^2+3y-4x+4y-12=0 \]
\[ xy-y^2-4x+7y-12=0 \]
Final Answer:
The joint equation is \(xy-y^2-4x+7y-12=0\), option (B).
\[ \boxed{xy-y^2-4x+7y-12=0\ \text{(B)}} \]