1) / sin x / = y ≥ 0 ;
We solve the equation

a = 1 ; b = 1 ; c = - 2 ;

y1 = ( - 1 + 3 ) / 2 = 1 ≥ 0 ( correct ) ;
y2 = ( - 1 - 3 ) / 2 = - 2 ≥ 0 ( false ) ;
Then, / sin x / = 1 ;
sinx = + 1 or sin x = - 1 ;
x ∈ { 90 } U { 270 } ;
x ∈ {90 , 270}.
Sorry, I guess I was in a hurry. This is how I did it after carefully reading the problem.
9.54% times which mobile phone (the one we are looking for=y) would use 1.908
that is: 0.0954 times y=1.908
0.0954y=1.908 dividing each side by 0.0954, we get y=20
So, the answer is y=20, or the mobile phone is 20
ANSWER

EXPLANATION
The given matrix is a 4 by 4 matrix.
We want to find

This is the entry in Row 1 Column 4.
We trace row 1 Column 4 and identify the entry in their intersection.
This entry is 5

It’s D it’s substitution just not simplified