Question 446332
{{{sqrt(40)+sqrt(90)}}}
={{{sqrt(4*10)+sqrt(9*10)}}}
={{{2*sqrt(10)+3*sqrt(10)}}} ... i.e. 2x+3x=5x
={{{5*sqrt(10)}}}
...
The answer would be 15.8 but, you could have found that from the beginning.  {{{5*sqrt10}}} is the simplified answer from what you gave.