The U.S. economy grew at a solid 6.4% rate in the first three months of this year, setting the stage for what economists are forecasting could be the strongest year for the economy in growth led by strong consumer spending. The Commerce Department said Thursday that growth in the gross domestic product, the country’s total output of goods and services, was unchanged from two previous estimates. It came after growth at a rate of 4.3% in the fourth quarter. Economists believe GDP growth will accelerate in the current April-June quarter to an annual rate of 10% or better. For the whole year, the economy is expected to grow by around 7%.