Aplico la estrategia para determinar si 105 es divisible entre 5,6 y 15​

Acompany wants to reduce the dimensions of its logo by one fourth to use on business cards. if the area of the original logo is 4 square inches, what is the area of the logo that will be used on the business cards?

X+ y = 5 ; x - y =3 solve using linear combination

Idon't get undoing if its pass adding and subtracting so can someone ? x-2 over 5 = 18