The answer is b because there is a negative in the exponent and the number needs to be a single digit and 54 is double digit. hope this helps!
a.

is a proper joint density function if, over its support,
is non-negative and the integral of
is 1. The first condition is easily met as long as
. To meet the second condition, we require

b. Find the marginal joint density of
and
by integrating the joint density with respect to
:


Then


c. This probability can be found by simply integrating the joint density:


Can you list the answer choices?

would be equivalent
Left one i think thats the one