X + Y : Y + Z
5 units : 2 units

X : Z
3 parts : 1 part

Since Y = 30 cm², this means that:

5 units – 30 = 3 parts — (1)
2 units – 30 = 1 part — (2)

(2) × 3: 6 units – 90 = 3 parts — (3)

(1) = (3): 5 units – 30 = 6 units – 90
6 units – 5 units = 90 – 30
1 unit = 60

Area of smaller square = Y + Z = 2 units

2 units = 60 × 2
= 120 cm²