He receives 3 dollars per week as allowances and an additional 1.75 dollars for each chore done by him.
His total earnings in one week would be sum of his allowances and chores that he complete in one week.
Here 't' represents total earnings and 'c' represents number of chores that he completed in one week.
Total Earnings = Allowances + (compensation of one chore)*(Number of chores)
Mathematically, it can be written as :-
t = 3 + 1.75c
Hence, (t = 1.75c + 3) is the required equation.