Question 47406
If I am reading it the right way, it is;
First you need all of them to be like terms so you can add or subtract.
So, since 63 is not a perfect square you need to find the multiples that are. 
63: 3, 7, 9, 12; 9 is a perfect square so; {{{sqrt(9*7)}}}, now look at {{{2sqrt(28)}}}, 28 is not a perfect square so find multiples that are; 2,4,7,14: 4 is or perfect square, so we have; {{{2sqrt(4*7)}}}, and finally {{{5sqrt(7)}}},
7 is not a perfect square, but it does not have any multiples that are so we can not do anything to that. Now we have;
{{{sqrt(9*7)}}}-{{{2sqrt(4*7)}}}+{{{5sqrt(7)}}}
find the square roots of the perfect squares;
{{{sqrt(9*7)}}}, 9 is a perfect square = 3, {{{sqrt(4*7)}}}, 4 is a perfect square=2; so now we have;
{{{3sqrt(7)}}}-{{{2(2)sqrt(7)}}}+{{{5sqrt(7)}}}, now you can add and subtract because they are like terms.
3-4+5=4; so the answer:
{{{4sqrt(7)}}}
Hope you understand :)