Gene length and GC content

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Hi All,

I am very new to DNA seq data. I have BRCA DNA seq data from National Cancer Insistitute. I have gene name/ ID in the table. I would like to find out gene length and GC content for each gene to perform some statistical analysis. Could someone please advice on how can I calculate these parameters? I am familiar with R packages, if that helps.
Your guidance is highly appreciated.

Thank you,
Sithara