To simplify the expression 2/(√7-√6)-√28+√54, we can start by simplifying the square roots.

√7 cannot be simplified any further, but √6 can be simplified as √(2*3) = √2√3.

So, the expression becomes:

2/(√7-√6)-√28+√54 = 2/(√7-√2√3)-√(4*7)+√(9*6)

Next, we can simplify the square roots further:

2/(√7-√2√3) = 2/(√7-√2√3) * (√7+√2√3)/(√7+√2√3)
= (2(√7+√2√3))/(7-2√6)

√(4*7) = √28 = √(4*7) = √4√7 = 2√7

√(9*6) = √54 = √(9*6) = √9√6 = 3√6

Now, the expression becomes:

(2(√7+√2√3))/(7-2√6) - 2√7 + 3√6

To simplify further, we can combine like terms:

(2√7 + 2√2√3)/(7-2√6) - 2√7 + 3√6

Now, we can simplify the denominator by multiplying the numerator and denominator by the conjugate of the denominator:

(2√7 + 2√2√3)(7+2√6)/(7-2√6)(7+2√6) - 2√7 + 3√6

Expanding the numerator and denominator:

(14√7 + 14√2√3 + 4√14√3 + 4√2√6)/(49 - 24√6 + 4√6 - 24)

Simplifying:

(14√7 + 14√2√3 + 4√14√3 + 4√2√6)/(25 - 20√6)

Now, we can combine like terms in the numerator:

(14√7 + 4√14√3) + (14√2√3 + 4√2√6)/(25 - 20√6)

Finally, we have simplified the expression to:

(14√7 + 4√14√3) + (14√2√3 + 4√2√6)/(25 - 20√6)