Daniel B. answered 11/12/21
A retired computer professional to teach math, physics
If you add up the given values for t and for u, you get a vector containing m and n.
And you are told that that vector equals (1,1).
That gives you equations for m and n.
t + u = (m+2, 3+n) = (1,1)
m+2 = 1 therefore m = -1
3+n = 1 therefore n = -2