For each of the following independent situations, prepare journal entries to record the initial transaction on December 31 and the adjustment required on January 31.

a. Magnificent Magazines received $12,000 on December 31, 2018, for subscription services related to magazines that will be published and distributed in January through December 2019.

b. Walker Window Washing paid $1,200 cash for supplies on December 31, 2018. As of January 31, 2019, $200 of these supplies had been used up.

c. Indoor Raceway received $3,000 on December 31, 2018, from race participants for providing services for three races. One race is held January 31, 2019, and the other two will be held in March 2019.