Question 285967
{{{7*sqrt(90) = 7*sqrt(9*10)}}}
{{{7*sqrt(9*10) = 7*sqrt(9)*sqrt(10)}}}
{{{7*sqrt(9)*sqrt(10) = 7*3*sqrt(10)}}}
{{{7*3*sqrt(10) = 21*sqrt(10)}}}
The answer is (2)