PLEASE HELP ME

Solve for c.
a(c + b) = d

The area of a circle is equal to 1 dm². find the radius of the circle.

Jessa bought a yoyo from a company that claims that, with each retraction, the string rolls up by 60% of the original length. she sets up a tape measure and throws the yoyo 3 times. her data are charted below. throw length of string (feet) 1 3 2 1.8 3 1.08 jessa wants to find the sum of the length of string after 10 throws. what is the sum of the lengths, rounded to the nearest hundredth?

The radius of the sphere is 10 units .what is the approximate volume of the sphere use π=3.14