We have the system of equations:

3c + 4m = 12.50 \tag{1} 3c + 2m = 8.50 \tag{2}

To find the cost of a slice of mushroom pizza (denoted by $m$), we can use elimination. First, subtract equation (2) from equation (1):

$(3c + 4m) - (3c + 2m) = 12.50 - 8.50$

This simplifies to:

$2m = 4.00$

Now, solve for $m$:

$m = \frac{4.00}{2} = 2.00$

Thus, the cost of one slice of mushroom pizza is $2, which corresponds to option D.

Would you like further details on how to solve this or explore related concepts?

Here are 5 related questions for further practice:

1. What is the cost of one slice of cheese pizza in this problem?
2. How would you solve this using substitution instead of elimination?
3. What happens if both types of pizzas had the same price?
4. How can you verify the solution once found?
5. How would this problem change if Jack bought 5 slices of mushroom pizza instead of 4?

Tip: Elimination works best when the coefficients of one variable are the same in both equations.