Does anyone know what the system of equations for this would be?

A + b = 10 pounds
rewrie as:
a = 10 pounds  - b

0.75a + 0.50 b = $6.00
replace a with the above equation:

0.75(10-b) +0.50b = 6.00

distribute the(10-b):

7.50 - 0.75b + 0.50b = 6.00

combine like terms:

7.50-0.25b = 6.00

subtract 7.50 from each side:

-0.25b = -1.50

divide both sides by 0.25 to find b
b = -1.50 / -0.25
b = 6 

she bought 6 pounds of bananas and 4 pounds of apples