KENNEBUNKPORT, Maine (AP) — Former first lady Barbara Bush is promoting literacy on her 90th birthday.

Bush is lending her backing to a $7 million challenge by X Prize and Dollar General. They're challenging developers to create a mobile app to help improve adult literacy skills.

The original X Prize was awarded 11 years ago for privately funded, suborbital flight. Since then, there have been other X Prize competitions aimed at spurring innovation.

Bush family members — including her son, former Florida Gov. Jeb Bush, who is expected to announce his presidential run next week — are in Kennebunkport for her birthday on Monday. A gala is planned for Monday night and a tent has been erected on the grounds of St. Ann's Church.