The product of 3, and a number increased by 6, is -24

This translates into mathematical language as follws:

 

the product of two numbers is found by multiplying them;

the two numbers are     '3'    and   'a number increased by 6';

'a number increased by 6' translates as 'x+6' or 'n + 6';

so the product is 3 times (x+6), which you write as 3(x+6);

'is' translates as '=', 'equal to';

so the final mathematical sentence for the given English sentence is:

                                         

                                                    3 (x+6)= - 24.