a=3cm в=0,7m m=300г

It looks like you're dealing with some measurements. However, to provide a helpful response, I'll need some context about what you're trying to calculate or what problem you're working on.

For example, are you looking to find the volume, area, or a specific physical property? Here’s a brief overview of the measurements you provided:

• \( a = 3 \, \text{cm} \) (This could be a length if it's a side of a shape)
• \( b = 0.7 \, \text{m} \) (This could also be a length, which you may want to convert to cm: \( 0.7 \, \text{m} = 70 \, \text{cm} \))
• \( m = 300 \, \text{g} \) (This is a mass)

Please provide more details about the problem, and I'd be glad to help!