Question 118064
In general, sqrt(a)*sqrt(b)=sqrt(a*b).
So for the first problem, simply multiply the 13 and 5 to get sqrt(65).  Now you need to see if this can be simplified by dividing by a perfect square.  Is it divisible by 4, 9, 16, 25, 36, 49, 64?  Nope.  So sqrt(65) is simplified.
The second part is more complicated because you need to distribute.  This works the same as something like x(3x+5x).  You multiply the outside by both parts.  So sqrt7(2sqrt3+3sqrt7)=2sqrt21+3sqrt49.  Now simplify: 2sqrt21+3*7 = 2sqrt21 + 21