Answer:
121
Step-by-step explanation:
31+90 = 121
180 - 121 = 59
180 - 59 = 121

Step 1:

Step 2:

On comparing values we get:
Taking:

n-5=0
n=5✓
or
Taking:

n-4=1
n=5✓
13. Greatest common factor means the largest number (greatest) you can divide (factor) into both numbers (common). So 13/13 is 1 and 65/13 is 5. The greatest common factor is 13.