we have that
3^y = 7
applying log both members
log(3^y)=log 7
y*log 3=log 7
y=log 7/log 3
using the logarithmic graph of y=log x
I graphically determine the values for x = 3 and x = 7
see the attached figure
for x=3
log 3=0.48
for x=7
log 7=0.85
therefore
y=log 7/log 3-----> y=0.85/0.48-----> y=1.77
the answer is
the approximate value of y is 1.77
