Parametric ray intuition

We can parameterize the ray from $C$ through $P$ as a function of $t$: $\qquad R(t) = (1-t)C + tP$ Using the graph below, find the value of $t^*$ such that $R(t^*) = I$. $t^* =$ [[☃ numeric-input 1]] [[☃ interaction 1]]