Liam is solving the equation 7x+6(x+3)=83%0D%0A7%0D%0A%0D%0A+%0D%0A6%0D%0A(%0D%0A%0D%0A+%0D%0A3%0D%0A)%0D%0A=%0D%0A83%0D%0A. His steps are shown below. What mistake did Liam make while solving?

The mistake Liam made while solving is in the distribution of the 6 to both the (x+3) and the 3, which should result in 6x+18 instead of 6(x+3)+3.