180° about z takes (x,y,z) -> (-x,-y,z)
90° about x takes (x,y,z) -> (x,z,-y)
so, your two rotations take (x,y,z) -> (-x,z,y)... z axis top/bottom, x/y axis right/ left... A dice has 3 on the top, 4 bottom, 1 left, 2 right, 5 left back, 6 right back... after the above rotations what numbers are showing on the dice now?