is this triginometry or algebra?

a rectangle has a length 2√x cm and width √x cm

the length of the diagonal of the triangle is √45 cm

i) find the area of the rectangle

ii) the area of the square is twice the area of the rectangle

find the length of a side of the square.

for part i) i did the a^2 + 0^2 = h^2

then in the calc. i did 2√x got 2√5 then sq it and got 10 ,...then i

did √x got √5 then sq it and got 5 , added them and got 15 so then i did the hypotenuse thing and √45 and got 20, yeah i know you are prob wondering how i got that and to be honest so am i lol because i used a new calc. for this and when i repeated it on an older calc. of mine i got a different answer so the CORRECT answer was :

2x=18cm^2

part 2 was= 6cm, but i got the answer wrong for i) so i was confused