ANSWER :
15 different ways
EXPLANATION :
Recall the combination formula :
[tex]_nC_r=\frac{n!}{(n-r)!r!}[/tex]where r is taken from n items.
From the problem, we have 6 vegetables to choose from. So n = 6
And a customer is allowed to choose four vegetables. So r = 4
Using the formula above :
[tex]\begin{gathered} _6C_4=\frac{6!}{(6-4)!4!}=\frac{6!}{2!\times4!} \\ \\ =\frac{6\times5\times4!}{2!\times4!} \\ \\ =\frac{6\times5}{2} \\ \\ =3\times5 \\ \\ =15 \end{gathered}[/tex]