K = 19. When you follow order of operations you start with Parenthesis.
So, plug in 19 first. (19+3) = 22 and (19+1)=20.
From there, you multiply the number outside the parenthesis.
22 * 4 = 88 + 2 = 90
Do the math on the other side now.
20 x 4.5 = 90
Considering they both equal 90, your problem is complete, and your answer for K is 19.
I hope this helps (: