We know in rectangle all angles are equal to 90 degree i.e angle r = angle s = angle t =angle u = 90 degree.

Now consider triangle RSX,

We have angle a + angle s +angle b = 180 degree

or angle a +angle b = 90 (since angle s = 90 degree)

Similarly in triangle XYT we have

angle c + angle d + angle t =180 degree

or angle c + angle d = 90 (since angle t = 90 degree)

and in triangle YRU

we have angle e +angle f + angle u =180 degree

or angle e + angle f =90 (since angle u = 90 degree)

Now putting the values in we get (a+b) +(c+d) + (e+f) = 90+90+90 = 270