log 60=log 400-0.2d log3 求d?

log 60=log 400 -0.2d log 3
log 60=log 400 +log 3^(-0.2d)
60=(400)[3^(-0.2d)]
0.15=3^(-0.2d)
log 0.15=(-0.2d)log 3
d=(-log 0.15)/(0.2 log3)