Please help me work this problem

13a

Step-by-step explanation:

Given

9a + 3a + a ← are like terms, they all have the variable a

To simplify add the numeric parts of the terms, that is

= (9 + 3 + 1 )a ← note a has a coefficient of 1

= 13a

0.61 has 2 decimal places, so we put the decimal digits of 0.61, 61 over 1 followed by the number of zeroes equal to the number of decimal places, 

2:     61/1 = 61/100.