Carbon-$14$ is an element which loses $10\%$ of its mass every $871$ years. The mass of a sample of carbon-$14$ can be modeled by a function, $M$, which depends on its age, $t$ (in years). We measure that the initial mass of a sample of carbon-$14$ is $960$ grams. **Write a function that models the mass of the carbon-$14$ sample remaining $t$ years since the initial measurement.** $M(t) = $ [[☃ expression 1]]