Question

Math question ,how ?

Answer 1

height of the screen = x
height of the shadow =
`(3)/(4)x`

ΔAEC ∼ ΔADB ⇒


`(BD)/(AB)= (CE)/(AC) \\ \\ (15)/(30)= ( (3)/(4)x )/(90+30) \\ \\ (1)/(2)= ( (3)/(4)x )/(120) \\ \\ (3)/(4)x = (120*1)/(2)=60 \\ \\ x=60: (3)/(4)=60* (4)/(3)=20*4=80 \ cm`

Height of the screen is 80 cm.

Answer 2

Let x be height of the shadow
30/15 = 90/x
Do cross multiplication
30x =1350
x = 45

Let h= height of the screen
1/4 of 45 is 11.25
H = 11.25 + 45
H= 56.25

There's your answer. I hope I did it right.