1) According to the law of conservation of momentum ..
Horiz recoil mom of gun (M x v) = horiz. mon acquired by shell (m x Vh)
1.22^6kg x 5.0 m/s = 7502kg x Vh
Vh = 1.22^6 x 5 / 7502 .. .. Vh = 813 m/s
Barrel velocity V .. .. cos20 = Vh / V .. ..V = 813 /cos20 .. .. ►V = 865 m/s
2) Using the standard range equation .. R = u² sin2θ /g
R = 865² x sin40 / 9.80 .. .. ►R = 49077 m .. (49 km)