Given:
Total salary of three persons a, b and c is Rs. 144000.
They spend 80%, 85%, and 75% respectively.
Their savings are in the ratio 8:9:20.

To Find:
C's salary.

Solution:
Let's assume the salaries of persons a, b, and c as A, B, and C respectively.

Step 1: Calculate the savings of each person.
- The savings of person a = (100 - 80)% = 20% of A
- The savings of person b = (100 - 85)% = 15% of B
- The savings of person c = (100 - 75)% = 25% of C

Step 2: Write the equation for the given ratio of savings.
- The ratio of savings of a : b : c = 8 : 9 : 20

Step 3: Set up the equation for the sum of the salaries.
- A + B + C = Rs. 144000

Step 4: Calculate the savings of each person in terms of their salaries.
- Savings of a = 20% of A = (20/100) * A = 0.2A
- Savings of b = 15% of B = (15/100) * B = 0.15B
- Savings of c = 25% of C = (25/100) * C = 0.25C

Step 5: Use the equation from Step 2 to express the savings of a, b, and c in terms of their salaries.
- 0.2A : 0.15B : 0.25C = 8 : 9 : 20

Step 6: Simplify the equation by multiplying each ratio by the least common multiple (LCM) of the denominators.
- 0.2A * (20/5) : 0.15B * (20/3) : 0.25C * (20/5) = 8 * (20/5) : 9 * (20/3) : 20 * (20/5)
- 0.8A : 1B : 4C = 32 : 60 : 80

Step 7: Divide each ratio by the greatest common divisor (GCD) to simplify the equation further.
- 0.8A/8 : 1B/20 : 4C/80 = 32/8 : 60/20 : 80/80
- 0.1A : 0.05B : 0.05C = 4 : 3 : 1

Step 8: Set up the equation using the sum of the salaries.
- 0.1A + 0.05B + 0.05C = 1

Step 9: Substitute the values from the equation into the equation from Step 3.
- 0.1A + 0.05B + 0.05C = 1
- 0.1A + 0.05B + 0.05(144