A
2D = 3C-0.1
we can not find D and C
so insuff


B
D+C=0.7
we can not find D and C
so insuff


A+B
two equn two unknows
we can solve for D and C
C=.3 and D=.4

Total lew spent 6$

we still can not find no of Ds bcoz
D and C can counter each other.


we can buy 3D or 4C in 1.2$...hence the exact number can not be determined...
hence insuff

so answer is E

Hope this helps

Let me know if u need a detailed explanation...

Let k be the donut price
Let x be the no of donuts

Let q be the the cupcake price
Let y be the no of cupcajes

Given: kx+qy = 6

Stmt I)

2k = 3q-.1

One eqn 2 vars INSUFF

Stmt II

k+q/2 = .7
k+q=.7

One eqn 2 vars INSUFF

Stmt I and II

2k=3q-.1
k+q = .7

We can find k and q but still not x and y

(FYI: It will be .4x+.3y = 6.0 1 eqn 2 variables)

E)

P.S Sometime one equation 2 variables can turn out sufficicent. Refer to
https://www.beatthegmat.com/logitech-ds2-t22368.html




In the DONUTS/CUPCAKE problem

x & y can have multiple values 12,4 or 9,8

So we dont know if its 12 donuts and 4 cupcakes or 9donuts and 8 cupcakes

INSUFF