Assignment
Not sure what any of that has to do with architecture, but setting that aside, the key here is to recognize that the 1 1/8" radius arcs at the ends are tangent with both the 2 7/8" radius and 5/8" radius arcs. Since the centers of all of those arcs align horizontally, the 1 1/8" arc is a semi-circle. The enhancements to Plate 6 below should get you going.
The easiest way would be to follow the instructions and draw circles. Then draw the two tangent lines. Then trim the circles, using the other circles and the lines as the cutting edges. The other thing to realize is that there are four centers, not three as stated in the instructions. Each of the four centers have two circles. The 1" diameter circles remain circles; the others get trimmed.