help!

Solution:

Since x and y are complementary they add up to 90degrees or PI/2 rads. 

$x+y = 90 \rightarrow (1)$

rearranging the terms we get:

 $y= 90-x$

Taking the sin on both sides we get the following identity:

$sin(y) = sin(90-x)$

$\Rightarrow sin(90)cos(x) - cos(90)sin(x)$

$\Rightarrow (1)(cos(x)) - (0)(sin(x))$

$\Rightarrow cos(x)$

$\Rightarrow -0.3$

$Answer: sin(y) = -0.3$