Answer: To solve the system of equations using substitution, we substitute the value of x from the first equation into the second equation.
Given:
Equation 1: x = 3
Equation 2: y = 7x + 4
Substitute x = 3 into Equation 2:
y = 7(3) + 4
y = 21 + 4
y = 25
Therefore, the solution to the system of equations is:
x = 3
y = 25