Let us say we have a density function : (inserted in pic down below).

To find the CDF from a density function, we can use any variable let us say B, to t (taking the integral); Because the CDF is : P[ T <= t] So that means all values for random variable T is less than little t, so to find the CDF in ANY case when given a PDF, we just take the integral of let us say B to t.

Now we know that from the picture. P[ T>5| T >2].

So this is infact the Survival function of T. P[T <=t]= 1- P[T>t]

so if we want to find the survival function, we just take the integral from t to infinity of the CDF.