There can be no such triangle. It can be shown that the minimum altitude
from R which a triangle SPR can have with an inscribed circle of
radius 3 and SP =7 is when such triangle SPR is isosceles. And that
is when the altitude from R is
or
. So
no such triangle can have an altitude from R as short as 15, as your
problem states.
The isosceles triangle SPR below is drawn to scale, with SP = 7,
and the inscribed circle has radius 3. Using similar right
triangles OBR and PAR, it's easy to show that AR =
.
Thus altitude RA cannot possibly be as short as 15, `for this is
the minimum case. You should point this out to your instructor.
There could have been a typo in one of the numbers.
Edwin