Help please. (right now i’m just filling in for the 20 characters it’s not relevant to the question)

9

Step-by-step explanation:

We're using the Pythagorean theorem here since it's a right triangle.

a^2 (side) + b^2 (side) = c^2 (hypotenuse)

12 = a

x = b

15 = c

12^2 + b^2 = 15^2

144 + b^2 = 225

- 144             - 144 (subtracting 144 from both sides to isolate b)

b^2 = 81

(getting rid of the exponent by squaring both sides)

b = 9

x = 9

= 5

step-by-step explanation:

to find the 15th term substitute n = 15 into the nth term formula

= (- 3 × 15 ) + 50 = - 45 + 50 = 5