Question

I forgot how to do this

Answer 1

Use the pythagorean theorem to find y.
a²+b²=c²
3²+4²=c²
9+16=c²
25=c²
c=5
y=5

All angles of a triangle form a sum of 180. We know there is 65 and 90 degree angles given to us. 
65+90+x=180
155+x=180
x=25