You can use the discriminant rule, which is :
b^2 -4ac
“exactly one solution” means that it is equal to zero
so:
b^2 -4(4)(9)=0
b^2 -4(36)=0
b^2 -144=0
b^2=144
square root both sides
b=12 or -12
hope this helps !
Given,
The salary for the technician from shop A is $900 per week.
The salary for the technician from shop B is $25 per hour.
The equation for the total pay for shop B is,

Taking the total pay as 900. As, to make the shop A and shop B equal.

Hence, he would have to log 36 hours during a week at Shop B in order to match the salary at Shop A.
when you have a linear combination for example 3x + 2y equals negative 4 you adieu like terms and then multiply