Three forces act on a 3 kg box: 10 N South-west, 17 N North-west, 5 N due East. What is the acceleration of the box?

find the N total

FtotalN=-10(.7)N+17(.7)+ 0 sum them
find the E total
sum them.

Now, net force=sqrt(Fn^2 + Fe^2)

a=netforce/mass