The equation can be rewritten as #(2sqrt(3)*3sqrt(5))-4sqrt(5)#.
#asqrt(b)*csqrt(d) -= (a*c)sqrt(b*d)#, so #2sqrt(3)*3sqrt(5) = (2*3)sqrt(3*5) = 6sqrt(15)#.
You now have #6sqrt(15)-4sqrt(5)#, as 15 has no factors which are perfect squares, #6sqrt(15)# cannot be simplified further, leaving you with #6sqrt(15)-4sqrt(5)#.