Mix variance and yield variance

Hello Sir,

Question is as follows:

To produce 19litres of Product X, a standard input mix of 8 litres of chemical A and 12 litre of chemical B is required.

Chemical A has a standard cost of $20 per litre and chemical B has a standard cost of $25 per litre.

During September, the actual results showed that 1850 litres of product X were produced ,using a total input of 900 litres of chemical A and 1100 litre of chemical B.

The actual costs of chemicals A and B were at the standard cost of $20 and $25 per litre Respectively.

Could you please show me total mix variance 2000 (Adv) for material A and yield variance 420 (Adv) for material A ?

Std cost of actual litres
$20* 900
Material mix variance

Std cost of total actual litres at std mix
$20*900/2000*8
Material yield variance

Std cost of actual production
8*£20*1850

Using the above steps could you please tell me where I am going wrong ?

Thanking you in advance