It is given that Roberts father is 5 years older than 3 times Robert's age which means that Roberts Father's age is 5 years more than 3 times the age of Roberts
∴ Roberts Father's age is: 3 times of Robert age + 5 years
Square root acts like a variable, so since there are 12 edges you want to distribute one length of an edge by 12. in the end youll get 144 + 120 square root 6