a triangular prism:):):):):)
The period of oscillation of a pendulum is

Where L is the length of the pendulum and

the gravitational acceleration.
Re-arranging the formula and using T=1.0 s, we find the length of the pendulum:
Find the ratio of the known sides 10 and 12
12/10 = 1.2
The larger kite is 1.2 times the size of the smaller kite.
Multiply 7 by 1.2:
x - 7 * 1.2
x = 8.4