5x=7+4y

Question

20x-16y=28

how many solutions are there for the system of equations?

Infinitely many solutions
No solution.
two solutions or three solutions?

Answer 1

5x=7+4y, so
5x-4y=7. Multiply both sides by 4, and you get:
20x-16y=28. But that's the other equation you were given - so you've actually only got one equation there, not two. And you can feed any value of x into that equation and get a corresponding value of y out.