Create an arc tangent to a line thru a point

One way (of many) to get what you want is with a fillet (basic curve menu). Choose the 2 curve fillet, choose the line you want the arc tangent to then choose point constructor and choose the point that you want the arc to go through. Finally, pick the approximate center point of your arc to pick which arc you want.

In version 18 This could be done by sketching the curves as basic curves which allowed you to do tangent arcs as you sketched the arcs. YOu could also bysect an angle in a similar manner. If you want to dimension the basic curves just use the add to sketch option in sketcher. You should be able to find the icon I think it shows lines circles and a + sign or at least it used to.

Fillet option as discribed by cowski is a good method also but if you can use basic curves for a quick way to get the geometry and add to sketch I've found this helpfull using a combination of Basic Curves and Sketcher.

Michael