Question

X = 8, y = 20. Find y when x = 42

Answer 1

8 / 20 = 42 / y;
Then, y = ( 42 × 20 ) / 8 ;
y = 840 / 8 ;
y = 105;

Answer 2

Create proportions to do this question
When x is 8, y is 20
when x is 42, y is ?

$\frac{8}{20}$ = $\frac{42}{?}$

Do cross multiplication:

8 × ? = 20 × 42
8 × ? = 840

Divide by 8 to isolate the unknown

$\frac{8*?}{8}$ = $\frac{840}{8}$
8 and 8 cancels out

? = 105

y is 105 when x is 42