:( PLEASE HELP ME

A mad scientist mixes Solution A and Solution B to create Solution C.
Solution C is 90 ml in volume and 40% acid (by volume).
Solution A is 20% acid.
Solution B is 50% acid.
How much of each solution is needed to create the final mixture C? Which system of linear equations would you use to set up the problem? Solve the system afterwards.

A. A + B = 90
.2A + .5B = .4(90)

B. A+B = 90
.2A + .5B = .4

C. A + B = 36
.5A + .2B = .4

D. A + B = .4 (90)
.2A + .5B = .4( 90)