please help. The figure below is a triangle with three unknown angles.

recall what a sum is: the addition of all values!
it's ok that they didn't give us specific values for each angle, plus we're not expected to do so! (notice how you can plug in only values m<1, m<2, m<3, there's no angle number like 45* or 23*, etc!)
so it's
m<1 + m<2 + m<3