How can i solve this simultaneous equation? (Lumda λ =1.42)

Additional info:(Lumda λ =1.42), i need to solve for m and n..

At the place where you got stuck, the equation has the form:

A - ½ = B

where A and B are complicated expressions. Just square both sides:

(A - ½)^2= B^2

A^2 - 2(A)(½) + (½)^2 = B^2

Then can simplify and solve for n.