How many substitutes can be found for the equation 3y + 5 - 2y = 11

Zero

One

Two

Infinitely many

We can solve the equation to find it's number of solutions, but we already know it only has 1 solution because it is a linear equation (y is raised to the first power).

3y + 5 - 2y = 11

y + 5 = 11

y = 6

This confirms that there is only 1 solution.