Answer:
Infinitely many.
Explanation:
y = 3x + 4
2y = 6x + 8
Basically you would fill in the variable for y into the second equation.
2 (3x + 4) = 6x + 8
Multiply 2 by the part in the parenthesis.
2 * 3x = 6x
2 * 4 = 8
Set up the equation and solve
6x + 8 = 6x + 8
Because the sides are the same, they cancel each other out. When two sides equal the same variable they have infinitely many solutions.