n=16

sqrt(20)+sqrt(500)+sqrt(80)=nsqrt(5)

Switch around terms

n*sqrt{5}=sqrt{20}+sqrt{500}+sqrt{80}

Find radicals of sqrt{20}, sqrt{500} and sqrt{80}

sqrt{20}= 2 sqrt{5}

sqrt{500} = 10 sqrt{5}

sqrt{80} = 4 sqrt{5}

Then add radicals together

n*sqrt{5}=16sqrt{5}

Divide by sqrt{5}

n=16