Assume that there are 2 trials.

x = 2 where x represents the number of successes.

which probability matches the probability histogram?

round the answer to one decimal place.

p(success)=0.3

p(success)=0.4

p(success)=0.6

p(success)=0.7

The p(success) = 0.6

Your question is a little unclear, but I believe you are asking about the probability that at least one of the trials in the experiment were successful.

If that is the case, you simply have to add the probability of 1 success with the probability of 2 successes.

That is 0.48 +  0.16 = 0.64

Rounding our answer to one decimal place gives us 0.6.

The correct answer on the test was

P(success)=0.4