(19) Another spacecraft that uses Plutonium-238 to generate electricity is the Voyager 1 spacecraft, which launched in 1977. If Pu-238 has a half-life of 87.7 years, what percent of the nuclear fuel remains in the RTG aboard Voyager 1 today? Show your work. [Hint: Use the equation N = e^(-0.008 t)] (20) How many years will pass before 25% of the Pu-238 in Voyager 1 remains? Show your work or explain your reasoning.

Simplifying

4x + 9 + -2 = 35

Reorder the terms:

9 + -2 + 4x = 35

Combine like terms: 9 + -2 = 7

7 + 4x = 35

Solving

7 + 4x = 35

Solving for variable 'x'.

Move all terms containing x to the left, all other terms to the right.

Add '-7' to each side of the equation.

7 + -7 + 4x = 35 + -7

Combine like terms: 7 + -7 = 0

0 + 4x = 35 + -7

4x = 35 + -7

Combine like terms: 35 + -7 = 28

4x = 28

Divide each side by '4'.

x = 7

Simplifying

x = 7

Explanation: