So let’s give each letter a variable

If b is 90% of c that means:

b=.9c

If a is 30% of C that means:

a=.3b

So take that second equation (a=.3b), and use the first equation to plug in for b. We get:

a=.3(.9c)

.3*.9=.27 which means:

a=.27c

.27=27%

ANSWER:

a is 27% of c

If you want to check you could give c a number.

Let’s say c=100

If b is 90% of c that means . 9(100)=b

.9(100)=90=b

To get a, multiply b by 30%

.3(90)=27=a

It checks out because 27 is 27% of 100