Let F be a field of characteristic zero. We give the following answer to a generalization of a problem of Büchi over F [t]: A sequence of 92 or more cubes in F [t], not all constant, with constant third difference equal to 6, consists of cubes of successive elements x, x+1, . . . , for some x ∈ F[t]. We use this, in conjunction to the negative answer to Hilbert's tenth problem for F [t], to show that the solvability of systems of degree-one equations, where some of the variables are assumed to be cubes and (or) nonconstant, is an unsolvable problem over F [t].