let
x-------> walnuts that Mario eats in a week
y-------> walnuts that Yolanda eats in a week
we know that
x=2y-------> equation 1
y=6*7-------> y=42 walnuts
substitute the value of y in equation 1
so
x=2*42-----> x=84 walnuts
therefore
the answer is
Mario eat in a week 84 walnuts
