Question 195221
Applying "log rules":
log7 x + log7 (4x+21) = 3
log7 x(4x+21) = 3
x(4x+21) = 7^3
4x^2 + 84 = 343
4x^2 + 84 - 343 = 0
Solving using the quadratic equation yields:
x = {3.5, -24.5}
Throw out the negative solution leaving:
x = 3.5
.
Details of quadratic follows:
*[invoke quadratic "x", 4, 84, -343 ]