Aalut ma puteti ajuta la cateva exercitii de matematica ?

Aflati valoarea numarului a

a)5+15×(25-75÷5+25:a)=1150:5 a=?

b)3+2×{[72-12×(a-3)]-9×4}=27 a=?

Ajutatima va rog frumos !! Multumesc anticipat!

a)

5 + 15 × ( 25 - 75 : 5 + 25 : a ) = 1 150 : 5

5 + 15 × ( 25 - 15 + 25 : a ) = 230

15 × ( 10 + 25 : a ) = 230 - 5

10 + 25 : a = 225 : 15

10 + 25 : a = 15

25 : a = 15 - 10

25 : a = 5

a = 25 : 5

a = 5 → numarul aflat prin metoda mersului invers

b)

3 + 2 × { [ 72 - 12 × ( a - 3 ) ] - 9 x 4 } = 27

2 x { [ 72 - 12 × ( a - 3 ) ] - 36 } = 27 - 3 = 24

[ 72 - 12 × ( a - 3) ] - 36 = 24 : 2 = 12

72 - 12 × ( a - 3 ) = 12 + 36 = 48

12 × ( a - 3 ) = 72 - 48 = 24

a - 3 = 24 : 12

a - 3 = 2

a = 2 + 3

a = 5