Simplify sqrt{28x} * sqrt{15x} * sqrt{21x}. Express your answer in simplest radical form in terms of x.

√ [28x] * √[ 15x ] *   √[21x ]   =

√[ 4 * 7 * x ] * √ [3 * 5 * x ]  * √ [3 * 7 * x ]  =

√4 * √7 * √x *√ 3 *√5 *√x *√3 * √7 *√x  =

2 * √x^3 * √3^2 * √7^2 *√5  =

2 * x √x *  3 * 7 *√5  =

42x √ [ 5x ]