(180:а+15×3):8=54:9
5×(810:9-x × 3)=40×8-5

(180:а+15×3):8=54:9(180 : a + 45) : 8 = 6
180 : a +45 = 6 * 8
180 : a + 45 = 48
180 + 45 = 45a
225 = 45 a
-45a=-225
a=5

5(810:9-x*3)=40*8-5
5(90-3x)=320-5
450-15x=315
-15x=315-450
-15x=-135
x=9