Minimum X-ray energy for Bragg reflection with n=1 in cubic crystal

[nmsurobert]

Homework Statement

A cubic crystal has a spacing between atoms of d = 0.2 nm. What is the minimum energy for X-rays such that non-trivial Bragg reflection may occur (peak with n =1)?
Write your answer in units of keV.

Homework Equations

2dsinθ = nλ

The Attempt at a Solution

i have no idea what I am doing. i don't remember the instructor talking about this nor can i find lecture notes on bragg reflection.
the only reason i know the "relevant equation" is because of a class i took semester where we did an experiment to show bragg reflection.

any advice would be appreciated. the second question is similar to this one.

 

[nmsurobert]

i found E = nhc/(2dsinθ)

if 2dsinθ = nλ then i do this ... E = (n(nhc))/2d and just plug numbers in?