Please answer correctly I’ll mark you brainlist!

5 cm

Step-by-step explanation:

since the last step in finding area of a triangle is divide by 2, multiply the area by 2 to get the original number

30 x 2 = 60

area/base = height

60/12 = 5

5

Step-by-step explanation:

Basically we need 60 because the area is 30, the formula to find area of a triangle is base times height times 1/2, so then 30 (area) times 2 is 60, then, 60 divided by 12 is 5. so your answer is 5!!

x^2 + 81

we can factor this using difference of square binomials.

rewrite the equation:

x^2 - (-81)

factor:

(a^2 - b^2) = (√a^2 + √b^2)(√a^2 - √b^2)

(x^2 - (-81) = (x + √-81)(x - √-81)

we can remove the - from under the radical by multiplying it by i.

(x^2 - (-81) = (x + i√81)(x - i√81)

(x^2 - (-81) = (x + 9i)(x - 9i)

we can check our answer by using foil:

x^2 - 9ix + 9ix - 81i^2

x^2 - 81^2

i^2 = -1

x^2 + 81