Answer:
35.1 units
Step-by-step explanation:
Imagine a right-angled triangle with RS as hypotenuse. The base would be 3 units and the height would be 6 units. By Pythagorus:
RS²=3²+6²
RS=≈6.7 units
Imagine a right-angled triangle with RT as hypotenuse. The base would be 9 units and the height would be 12 units. By Pythagorus:
RT²=9²+12²
RT= = 15 units
Imagine a right-angled triangle with TS as hypotenuse. The base would be 12 units and the height would be 6 units. By Pythagorus:
TS²=12²+6²
TS=≈13.4 units
Perimeter=RS+RT+TS
=6.7+15+13.4
=35.1 units