Can someone show me a step by step with the answer?

6 mols HCl

Explanation:

(I'm an AP chemistry student but not perfect at this stuff)

you can use the Molarity=Moles/L equation here:

(6M)=(moles HCl)/(1L)

divide by 1 on both sides to isolate the moles of HCl

this gets you 6 moles HCl.

Again I'm just a student so my answer might be wrong, but this question should just require the M=mols/L equation :).