Find `0.4 -: 2` and `651.2 -:4`

Find : 0.4 div 2

Find : 651.6-:4

.Find: (i) 0.4-:2

Find : (i) 0.4-:0.2

Find : 651.2 div 4

Evaluate: 35.9 - 2.1 xx 0.9 + 17.2 div 0.4 - 0.4

Find all common tangents of the pairs of circles x^(2) +y^(2) +4x + 2y -4 =0 and x^(2) +y^(2) -4x -2y +4=0