Defendant was entitled to new sentencing hearing, where Dist. Ct. had imposed 97-month term of incarceration without providing adequate explanation for why it imposed instant within-guidelines sentence. Fact that Dist. Ct. stated that it had “considered all the factors of 18 USC section 3553(a),” that defendant’s crimes were “serious,” and that it hoped defendant would take advantage of rehabilitation services while incarcerated, did not require different result. Ct. also rejected govt. argument that instant explanation was adequate where defendant offered only stock arguments for lower sentence that did not require specific response by Dist. Ct.