Write the exponential growth function

Devise the exponential growth function that ts the given data, then answer the accompanying question. Be sure to identify the reference point (t = 0) and units of time. Uranium-gas (U-238) has a half-life of 4.5 billion years. Geologists nd a rock containing a mixture of U-238 and lead, and determine that 75% of the original U238 remains; the other 25% has decayed Into lead. How old is the rock? What is the reference point (t: 0)? A. When the rock does not contain any more of the original amount of U-238. B. The state of the rock 4.5 billions years ago. { 5" C. When the rock contained 100% of the original amount of U-238. D. The current state of the rock with 75% of the original amount of U-238. What are the units of time? ~ ~ . 9V billions of years decades years months Write the exponential growth function. Use yo the initial value of y. ya) = [:1 (Type an expression. Round coeicients to three decimal places as needed.)