SAT Subject Test Mathematics Level 1

The answer is (E).

UNKNOWN IN AN EXPONENT

The procedure for solving an equation when the unknown is in an exponent is
a little different. What you want to do in this situation is to express one or
both sides of the equation so that the two sides have the same base. Look at
Example 7.

Example 7

1. If    8 x    =   16x–1,  then    x   =

(A)

(B)

(C) 2

(D) 4