I believe its lack of worthy projects, but ill tell you if im wrong.
Answer:
As agriculture increased, more farming machines were used.
It depends on what you're asking. If angle a and b are both on a straight line, b would equal 169 degrees because the total has to add up to 180 degrees, but if they are on a right angle, b would equal 79 because it has to add up to 90 degrees.
