Question explains itself in the picture.

30 cm

Step-by-step explanation:

Area of a triangle formula:

A = 0.5bh

Given:

b = 12

c = 5

Work:

A = 0.5bh

A = 0.5(12)(5)

A = 6(5)

A = 30

13 x 12= 156 x 5 = 780

Step-by-step explanation:

i dont know it

step-by-step explanation:

second option

step-by-step explanation:

the measures of a triangle equal 180. use that to find x.

2x+3x+4x=180

9x=180

9x/9=180/9

x=20

now you know x, you know angle a is 40°, angle b is 60°, angle c is 80°.

because angle a is 40°, the first option doesn't work.

because angle b is 60°, the second option does work.

when you add angle a and b, you get 100°. complementary means it equals 90°, so the third option doesn't work.

when you add angle a and c, you get 120°, which is not 100.