Is this context free
Strings over the alphabet {a,b,c,d} where there are at least 3 times as many b's as c's

I have worked this out to be context-free and not regular. But I just wanna confirm that I am correct. Hints will be greatly appreciated. 
Is this context free
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Strings over the alphabet {a,b,c,d} where there are at least 3 times as many b's as c's

I have worked this out to be context-free and not regular. But I just wanna confirm that I am correct. Hints will be greatly appreciated. 