Question

Help me on these please !

Answer 1

To go along with BrainGuide, try to work backwards. :) For example:
On 25, you would have 180-90=90. 3x=90. 90÷3=30. 2×30=60. Now check by adding once more. 30+60+90=180.

Answer 2

The 3 sum of the 3 angles in a triangle is 180 .
so
for 20.
X+65+50=180
21.
56+34+X=180
22.
90+53+X=180
24.
X+X+X=180
25.
X+2X+90=180
26.
X+X+25=180
now solve each as equations to find X