The monthly standing charge for a electrical company is €12.50 plus a cost of €0.16 per unit of electricity used.

I not sure but I think you do

156.18-12.50=
and then I think you divide the answer by 0.16

You're right.

To determine how many units of electricity the customer used in that month, we can subtract the standing charge from the total bill, and then divide the result by the cost per unit of electricity used.

Let's break down the calculations step by step:

1. Subtract the monthly standing charge from the total bill:
Total bill - Standing charge = €156.18 - €12.50 = €143.68

2. Divide the result by the cost per unit of electricity used:
€143.68 / €0.16 = 898 units

Therefore, the customer used 898 units of electricity in that month.

To calculate this on your own, you can use the formula:

Units = (Total bill - Standing charge) / Cost per unit of electricity used

This formula can be used to determine the number of units used for any given total bill and cost per unit of electricity used.