Consider a solution containing 37.0 (+/- 5)% (wt/wt) HCL in water. The density of the solution is 1.18 (+/- 0.01) g/mL. To deliver 0.0500 (+/- 3%)mol of HCL requires 4.18 (+/- x) mL of solution. Find x.

My teacher said x= .4.
How do you solve for uncertainty?

http://www.rit.edu/~uphysics/uncertainties/Uncertaintiespart2.html#muldiv

The errors add; see the propagation of errors section on that page.