g++ not found when using install_github

Question

I am trying to install an r-package via github via devtools::install_github('package_name')

I get the following error: "sh: g++ not found" and "ERROR: compilation failed for package 'package_name' "

Question: What do I need to do in order to have/find g++?

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Extra information:

• Windows 8.1 OS
• R version 4.1.0
• devtools version 2.4.2
• rtools 40 installed (find_rtools() -> TRUE)