Slope fields and Euler’s method practice question 8

Here the slope changes with time as well as with the population. At the start of each step, which two values do you need before you can work it out?

The slope depends on both $t$ and $P$: $f(t, P) = (0.6 - 0.2t)P$. Each step is $P_{k+1} = P_{k} + \Delta t\cdot f(t_{k}, P_{k})$.

The first step uses $(t_{0}, P_{0}) = (0, 100)$; the second uses $(t_{1}, P_{1})$, with $t_{1} = 1$.