The adjacent angles are proportional to the numbers 4 and 11. Find the difference between these angles ..

Given:
∠ (a1b) and ∠ (a2b) are adjacent;
∠ (a1b): ∠ (a2b) = 4: 11;
∠ (a2b) – ∠ (a1b) =?
Decision:
1) Let k be the coefficient of proportionality, then ∠ (a1b) is equal to 4k and ∠ (a2b) – 11k.
The sum of adjacent angles is 180 degrees, then:
∠ (a1b) + ∠ (a2b) = 180 °;
4k + 11k = 180 °;
15k = 180 °;
k = 180 °: 15;
k = 12 °.
If k = 12 °, then ∠ (a1b) = 4k = 4 * 12 ° = 48 °;
∠ (a2b) = 11k = 11 * 12 ° = 132 °;
2) ∠ (a2b) – ∠ (a1b) = 132 ° -48 ° = 84 °;
Answer: 84 °