I don't know how to solve 6 and 7 for the rate of change.

006 10.0 points A circle of radius r has area A and circum- ference C are given respectively by A = mr2, C = 2ar. If r varies with time t, for what value of r is the rate of change of A with respect to t twice the rate of change of C with respect to t? 1. T = 2. 1 = 3. 7 = 2 4. 7 = 27 5. 7 = 1 6. 7= 007 10.0 points The radius of a circle is increasing at a constant rate of 7 ft/sec. Express the rate at which the area of the circle is changing in terms of the circumfer- ence, C of the circle. 1. rate = TC sq. ft./sec 2. rate = 147C sq. ft./sec 3. rate = 7TC sq. ft./sec 4. rate = 14 C sq. ft./sec 5. rate = 7 C sq. ft./sec 6. rate = LC sq. ft./sec