The bill for repairing a washing machine came to £151.68, inclusive of vat at 20% what was the cost before vat was added show workings

You can write an equation and solve it.
The price before VAT is x.
VAT is 20% of the price, so VAT is 20% of x, or 0.20x.
When you add the price and the VAT, you get £151.68.
The price plus VAT is x + 0.2x. That must equal £151.68.

x + 0.2x = 151.68

Add like terms x and 0.2x.

1.2x = 151.68

Divide both sides by 1.2 to isolate x.

x = 126.4

The cost before VAT is £126.40.