Which of the following statements is logically equivalent to "if i study, then i get better grades"?
a. lf i do not study, then i do not get better grades.
b. if i get better grades, then i study.
c. if i do not get better grades, then i do not study.
d. if i get better grades, then i do not study.

The students at jefferson middle school are raising money for a charity by selling t-shirts and hats. the number of t-shirts sold was 3 times the number of hats. the profit was $5 for each t-shirt sold and $2.50 for each hat sold. the students raised $840 for the charity. they used the system below to analyze their success and found the solution to be (144, 48). 5x+2.50y=840 x=3y how much did they earn from t-shirt sales?