Determine the electric field intensity that enables the spheres to be in equilibrium at theta= 8�.?

Two 4.0 g spheres are suspended by 8.0 cm long light strings (Fig. P15.57) http://www.webign.net/sercp/p15-57.gif . A uniform electric field is applied in the x direction. If the spheres have charges of -7.0 10-8 C and +7.0 10-8 C, determine the electric field intensity that enables the spheres to be in equilibrium at = 8�.