Question 254153
60% is correct.
Here's why.
we are told that
x=40% of y
x=.4y
What percent of y is x
"what percent of"=40%
40%*y=x
.4y=x
we are asked "what percent of 2y is 3x?"
"what percent of"=a
a*2y=3x
we write that as 
3x=a*2y
where a is the percent
3x/2y=a
from the first equation we know that x=.4y
3*.4y/2y=a
y/y=1
.4/2=.2
3*.2=a
.6=a
.6=60%
a=60%

another way to solve it

x=.4y
3x=a*2y
multiply first by 3
3x=1.2*y
3x=a*2y
1.2y=a*2y
divide by y
1.2=2a
.6=a