log with a base of two and exponent of eight plus log with a base of two and exponent of sixteen.

Adding logs can be replaced by multiplying the numbers:

log₂8 + log₂16 =  log₂(8·16)  =  log₂(128)  =  log₂(2⁷)  =  7

or:  log₂8  =  3     and   log₂16  =  4      --->      log₂8 + log₂16 =  3 + 4  =  7