If frequency of radiation = 1.0 x 10¹⁵s⁻¹
Energy of radiation is equal to Planck's Constant(6.626 x 
10⁻³⁴ m² kg / s) multiplied by frequency
Energy of radiation=6.626 x 10
⁻¹⁹ J

An electron on the surface requires a certain amount of energy to free itself from the atom. That energy is (Threshold frequency x Planck's constant)
Energy to free electron=4.638 x 10⁻¹⁹ J

Kinetic Energy of electron= Energy of radiation - Energy to free electron

KE=1.988 x 10⁻¹⁹ J ≈ 2 x 10⁻¹⁹ J