"it costs $2200 to produce 100 chairs in one day" so, letting x be the number of chairs produced and letting y be the cost, x= 100, y= 2200 and the equation becomes 2200= 100m+ b.
"and $4800 to produce 300 chairs in one day." Okay, now x= 300 and y= 4800: 4800= 300m+ b.
Solve those two equations for m and b.
In fact, since the question only asks for the slope, m, use that fact that if you subtract one equation from the other, b cancels out.