I need help with this​

Evaluate the expression for the given value of the variable 7a - 4a for a =8

In the diagram, gef and hef are congruent. what is the value of x

Randy and trey take turns cleaning offices on the weekends. it takes randy at most 4 hours to clean the offices. it takes trey at most 6 hours to clean the offices. what is the greatest amount of time it would take them to clean the offices together? 2.4 hours 2.5 hours