Ответ ;

7/11 = 35/40 + 3z

7 × 40 + 3z = 35 × 11

280 + 3z = 385

3z = 385 - 280

3z = 105

z = 105 : 3

z = 35

____________________

7 × 40 + 3 × 35 = 35 × 11

385 = 385

ответ ; z = 35