The age of a father is 2 less than 7 times the age of his son. in 3 years, the sum of their ages will be 52. if the son’s present age is s years, which equation models this situation?

"the age of a father is 2 less than 7 times the age of his son"
"father" = "f"
"is" = "="
"2 less than" = "- 2"
"7 times" = "7 *"
"age of his son" = "s"

combine this and you get
F = 7S - 2

then we have "in 3 years"
so in 3 years
father would be (F + 3)
son would be (S + 3)
and if the sum of their ages equals 52
we get
(F + 3) + (S + 3) = 52

hopefully this gets you to your answer :)
if not, feel free to comment and I'll help you further ^_^