Back in the day, kids gobbled up Bush lyrics ("Blue asbestos in your veins/I'm your broken fingers," for example) like they were written by an alt-rock William S. Burroughs. Frontman Gavin Rossdale knew his audience. The high-school dropout once told an interviewer that the square root of 121 was 9, and neither he nor his fans had much use for the right answer. Musical retardation can be fun: All but one of Sixteen Stone's five hit singles were built on four simple chords — easy to learn on guitar and great to sing along with ("breathe in, breathe out . . . "). And even if Rossdale can't multiply 11 x 11, he used to be able to count to four. On his languid debut solo album, he plays the sensitive singer-songwriter, following Chris Cornell's belated and boring path to maturity. Good thing wife Gwen Stefani has a colossal career. Someone has to pay the bills.