In the expression 2x-15, what is the variable being used ?

Plz hurry evaluate the expression a+b where a=8 and b=19

Every weekday, mr. jones bikes from his home to his job. sometimes he rides along two roads, the long route that is shown by the solid lines. other times, he takes the shortcut shown by the dashed line. how many fewer kilometers does mr. jones bike when he takes the shortcut instead of the long route?

Simplify the given expression leaving the answer in improper fraction form. 2/3+5/6