Let k and d be the Kevin's age and the Daniel's age; We have the equation: k = 3 + d; k - 2 = 4( d - 2 ); We have 3 + d - 2 = 4d - 8; Then, d + 1 = 4d - 8; 9 = 3d; d = 3. Finally, k = 6 years.
But, given that Newton's Second Law is F=ma and since you are given the mass and force, the acceleration can be easily calculated by isolating variable acceleration (a)