Strobel, who retired on August 31, 2019, receives a monthly pension benefits of $2,000 payable for 15 years. The first pension check was received September 20,2019. During his years of employment, Strobel contributed $75,600 to the cost of his company's pension plan. How much of the pension amounts received during 2019 may Strobel exclude from gross income? a. $0 b. $1,680 C. $6,320 d. $8,000