Using the numbers 6, 12, 18, 36 and the operations -, +, (), /, each exactly once, find an expression that evaluates to 15.

Here are the solutions for each equation:

a) Target: 15
We need to use the numbers $6, 12, 18, 36$ and the operations $-, +, (), \div$ exactly once.

Step 1: Calculate $18 - 6$.

$$18 - 6 = 12$$

Step 2: Calculate $36 \div 12$.

$$36 \div 12 = 3$$

Step 3: Add the results from Step 1 and Step 2.

$$12 + 3 = 15$$

So, the equation is:

$$$$