Please Can Someone Help Me Solve For x Using Log Properties: log(base 3) x*(x-80)=4

log(base 3) x*(x-80)=4

3^4 = x(x-80)
81 = x^2 - 80
quadratic equation
x= -1(rejected) or 81
x= 81
log properties used=
log(base a)b=k
a^k=b
hope it helps :)