Let the number be 'a':
The difference of the square of a number and 4
a^2 -4
is equal to 3 times that number.
= 3*a
a^2 -4 =3a
a^2 -3a -4=0
(a-4) (a+1)=0
solutions are: 4 and -1
Look at the picture.
We have the equation (1) 12x + 4y = 40.
We know, the sum of the acute angles in a right triangle is 90°.
Therefore we have the equation (2) (12x + 4y) + (17x - y) = 90
Substitute (1) to (2):
40 + 17x - y = 90 <em>subtract 40 from both sides</em>
17x - y = 50 (3)
We have the system of equations:

Substitute the value of x to (3)

Answer: x = 3 and y = 1.