bonsoir
a. soit x le nombre cherché
x/4 + 13 = 20
x/4 + 52/4 = 80/4
x /4 = 80/4 - 52/4
x /4 = 28/4
4 x = 112
x = 28
28/4 + 13 = 20
7 + 13 = 20
b . (x + 4 ) / 13 = 20
( x + 4 ) /13 = 260/13
13 x + 52 = 3 380
13 x = 3 380 - 52
13 x = 3 328
x = 256
( 256 + 4 ) /13 = 20
260/13 = 20
20 = 20
