It's difficult to put a value on a painting of a girl picking apples by Robert Wood. Firstly, without seeing the painting, it's impossible to know what condition it's in, and this can alter the value dramatically.
That being said, if we look at the current market, we can make a fairly accurate guesstimate.
The majority of Robert Wood paintings on auction sites such as eBay sell for around £5-£25. That's not to say that your painting couldn't be worth more, but this is an indication of how highly Robert Wood's paintings are considered by the general public.
What should you do?
I'd recommend seeking the advice of a professional to truly discover the value of your Robert Wood painting. A professional will assess the authenticity of the piece, along with the condition and any other factors that may alter the overall value.
If you're unlikely to receive a big sum for your painting, you could always put it up for auction on eBay and hope that someone really likes the look of it. I'm always surprised at the type of things people really want to buy on eBay, and there's definitely people out there that will buy a nice looking painting, even if it's not worth loads.
Who knows - maybe you've picked up a hidden gem like some of these lucky people!