How to solve this non-linear equation This came from a regression: $$\text{Diameter} = 0.0531052 + 0.0443237 \cdot \exp (-0.0103633 \cdot \text{'Time elapsed'})$$ if diameter is $-0.052$ What will be time elapsed, can someone help me?

You have

$$D_i = -0.0531052 + 0.0443237\exp(-0.0103633\Delta t)$$

Solve for $\Delta t$ to obtain

$$\Delta t = -\dfrac{1}{0.0103633}\ln\dfrac{D_i+0.0531052}{0.0443237}$$