How would i create a real life situation where i would need equation with variable on both sides to solve it. then how would i explain in words on how the problem was solved. i need at least 8-10 sentences but i need

A social networking site recorded that 80 % of the people who became members of the site one month were between 30 to 40 years old. The equation below represents this information, where x represents the total number of people who became members of the site that month:
x = 0.8x + 72
How many people who became members of the site that month were between 30 to 40 years of age?