Answer:
[tex]\bold{\underline{a_n=18n-15}}[/tex]
Step-by-step explanation:
[tex]a_n=a_1+d(n-1)\\\\a_5=a_1+d\cdot4\\\\a_7=a_1+d\cdot6\\\\a_7-a_5=a_1+6d-(a_1+4d)=2d\\\\111-75=2d\\\\2d=36\\\\d=18\\\\\\a_1+18\cdot4=75\\\\a_1=75-72=3\\\\\\a_n=3+18(n-1)=3+18n-18\\\\\underline{a_n=18n-15}[/tex]
