Your diagram didn't show up, but I'll take a guess.
There are 2 cogs, connected together by a belt.
Find the length of the belt.
The large cog has a radius of 11cm. The small cog has a radius of 4cm.
The distance between the centres of the 2 cogs is 25cm.
I got . and .
These happen to be correct.
In the diagram, consider quadrilateral
. . Note that it has two right angles.
| @ *
7 | * 25
Q * - - - - - - - - - * P
| 24 |
4 | | 4
B * - - - - - - - - - * Z
In right triangle
Can you finish up?