Answer:
Step-by-step explanation:
By the triangle sum theorem, the sum of angles in a triangle is equal to 180°. Therefore, m∠A + m∠B + m∠C = 180°. Using the Substitution property
(6x)° + 90° + (x+6)° = 180°
To solve for x, first combine the terms to get (7x + 96) = 180°
Using the Subtraction property of equality,
7x = 84.
Then using the division property of equality x = 12.
To find the measure of angle A,
Use the subtraction property to get m∠A = 6(12)°.
Finally simplifying the expression gets m∠A = 72°.
since the triangular pyramid has 4 faces and each has an area of 30 
we should multiply that by 4 , so :