Answer:
The radius will be half of your diameter so,
since 26 is your diameter half of that is = 13 is your new radius.
Now finding the area:
13^2 = 169
169 x 3.14 = 530.66 cm2 is your area.
Formula of an area of a circle:
πr^2
pi(3.14 or 22/7 depending on whatever they tell you to use for pi) x radius being squared