Answer
39 - B. 31.4
40 - C. 9.8x+1.1y+9.9z
For 39, the formula for the circumference of a circle is [tex]2\pi r[/tex] where r is the radius of the circle. Substituting r=5 gives [tex]2\pi 5=31.4[/tex].
For 40, you basically just add up like terms according to which variable the coefficient is in front of.
[tex]5.5x+4.3x=9.8x\\6.2y-5.1y=1.1y\\8.3z+1.6z=9.9z\\9.8x+1.1y+9.9z[/tex]
Hope this helps.
