Aparticular computer takes 43 nanoseconds to carry out five sums and seven products. it takes 36 nanoseconds to carry out four sums and six products. how long does the computer take to carry out one sum? to carry out one product?

Sums→x
Products→y

Computer takes 43 nanoseconds to carry out five sums and seven products: 5x+7y=43
It takes 36 nanoseconds to carry out four sums and six products: 4x+6y=36

5x+7y=43
4x+6y=36⇒4x=36-6y

5x+7y=43
x=9-1.5y

5*(9-1.5y)+7y=43⇒45-7.5y+7y=43
x=9-1.5y

0.5y=2⇒y=4
x=9-1.5*4⇒x=3

Computer takes 3 nanoseconds to carry out one sum and 4 nanoseconds to carry out one product.

The answer is option c.