Every angle answer you write should look the same shape: angle = number, reason. That's the whole method. The number comes from the maths; the reason comes from naming the fact you used.
The Three Moves
One — read the diagram, not the picture. Look at the marks: arrows mean parallel, ticks mean equal, the little square means 90°. The angle facts you're allowed to use depend entirely on what's marked.
Two — do the calculation. Spot which fact connects your known angle to the unknown, and run it. Sometimes that's a subtraction (180 − 70), sometimes it's just "they're equal".
Three — write the reason beside it. Not in your head — on the page. "Co-interior angles, parallel lines." "Vertically opposite angles are equal." The reason is a mark.
A Worked One, Set Out Properly
Two parallel lines, a transversal, one angle marked 110° on the inside. Find x on the inside below it:
x = 180° − 110° = 70° (co-interior angles, parallel lines)
That single line earns both marks: the right value and the named reason. Leave the reason off and you've thrown half the marks away even with the right number.
Learn the Reasons Word-for-word
Examiners want the proper phrase, not a vague gesture. "Co-interior angles, parallel lines." "Corresponding angles, parallel lines." "Alternate angles, parallel lines." "Angles on a straight line." "Vertically opposite angles." Drill them in the toy — it checks the number and the reason separately, so you'll feel straight away when one's missing.