Answer:
x = -log 6/log 5
Explanation:
When the variable is in te exponent, logarithms help solve the equation very often.
5^-x = 6
Take the log of both sides.
log (5^-x) = log 6
Use the law of log of a power.
-x log 5 = log 6
-x = log 6/log 5
x = -log 6/log 5