Find the exact solution to: ln(x) + ln(7) = ln(21)

Log rules:

log(a) + log(b) = log(ab)

so, in this case, we must find x such that 7x = 21

thus x = 3

similarly, log(a) - log(b) = log(a/b)

rearranging the original equation we get:

ln(x) = ln(21) - ln(7)

so x = 21/7 = 3