log_{2}7 * log_{7}4 =\frac{1}{log_{7}2} * log_{7}4 = \frac{1}{log_{7}2} * log_{7}2^{2}= \frac{1}{log_{7}2} *2log_{7}2 = 2
log_{2}7 * log_{7}4 =\frac{1}{log_{7}2} * log_{7}4 = \frac{1}{log_{7}2} * log_{7}2^{2}= \frac{1}{log_{7}2} *2log_{7}2 = 2