Can someone please explain it to me ASAP??!! This is exponential model

Devise the exponential growth function that fits the given data, then answer the accompanying question. Be sure to identify the reference point (t = 0) and units of time. Uranium-238 (U-238) has a half-life of 4.5 billion years. Geologists find a rock containing a mixture of U-238 and lead, and determine that 53% of the original U-238 remains; the other 47% has decayed into lead. How old is the rock? . . ... B. The current state of the rock with 53% of the original amount of U-238. O C. The state of the rock 4.5 billions years ago. VD. When the rock contained 100% of the original amount of U-238. What are the units of time? 4 (0/ billions of years 8 (0/1 O months O decades O years Write the exponential growth function. Use yo the initial value of y. y(t) = (Type an expression. Round coefficients to three decimal places as needed.)