This problem is about using the right order of operations. To do that we can recur to PEMDAS, which means Parenthesis, Exponents, Multiplication-Division, Addition-Subtraction, that's the order to solve this problem.
First, we solve parenthesis using the distributive property:
[tex]7x+6+5(4x+3)=7x+6+20x+15[/tex]Second, we solve like terms, that is, those terms which have variables, and those terms without variables.
[tex](20+7)x+15+6=27x+21[/tex]Therefore, the answer is 27x+21, that's the simplest form to the given expression.