Please help solve this area formula, thanks

A=1/2(Sqrt20)(Sqrt45)

A = 1/2 sqrt (4*5*9*5)
A = 1/2 * 2*3*5
A = 15

A = 1/2(√20)(√45)
Find factors of radicals which are perfect squares
A = 1/2(√4*5)(√9*5)
Take square roots
A = 1/2*2√5*3√5
multiply out
A = 1/2*2*3*√5*√5
A = 15

Checked with calculator - it's correct