Final answer:
The question involves solving a system of linear equations using the substitution method. The equations X = y - 7 and 3x - 4y = -24 are solved by substituting y - 7 for X in the second equation, resulting in X = -4 and y = 3 as the solution.
Step-by-step explanation:
The subject of this question is Mathematics, specifically focusing on the use of the substitution method to solve a system of linear equations. 
The given system includes the equations X = y - 7 and 3x - 4y = -24. Here's a step-by-step guide to solve the system using substitution:
- Start with the provided equations:
 X = y - 7 
 3x - 4y = -24 - Substitute the expression for X from the first equation into the second equation:
 3(y - 7) - 4y = -24 - Simplify and solve for y:
 3y - 21 - 4y = -24 
 -y = -24 + 21 
 -y = -3 
 y = 3 - Substitute the value of y back into the first equation to solve for X:
 X = 3 - 7 
 X = -4 
Therefore, the solution to the system of equations is X = -4 and y = 3.