Faced problems with regular expressions

Question

There are several options for writing lines. You need to get only the first digits and immediately standing letters behind them (if any)

425 ml (340 g)
(first digits 425) (first letters ml)

5*75 g
50.065 g
0.014
400 g
0.875 ml
1.45 l
145g. - 12 pcs
(first digits 145) (first letters g)

The task is to use as few regular expressions as possible to get a result of the form from these lines: 400 g

I've been scratching my head for a few days, please help me..