Show ur work its math

Last week , donnell practiced the piano 3 hours longer than marcus . together, marcus and donnell practiced the piano 11 hours . for how many hours did each young man practiced the piano

Ineed to know how to write question one in mathematical terms

Acontainer holds 0.7 liters of oil and vinegar. 3/4 of the mixture is vinegar. how many liters of oil are in the container? express your answer as both a fraction and a decimal.