Pass1: check _ character in place 2,7,12,17 of flag
Pass2: check 4th char of flag=0 | 6th char=3 | 14th char=0

other Linear Algebra is:
```
(1th+5F)+3th=0F4
(4th+5th)+6th=0D9=>(30+5th)+33=0D9=>5th=76='v' place5='v' [pass2]
(4th+5th)+6th =0D9 place4=0 | place5=v | place6=3 [pass3]
7th+8th+9th=10D => 5F+8th+9th=10D=> 8th+9th=10D-5F=AE if place 8='5'=> place9=>79='y'
```
...

```
x10=a [10th char of flag]
x11=b
x13=c
x15=d
x16=e
x18=f
```

```
a+b=188
c+d=210
e+f=201
a+c+e=332
d+f=195
a+e=232
```

solve Linear Algebra with:
`https://quickmath.com/webMathematica3/quickmath/equations/solve/advanced.jsp#c=solve_advancedsolveequations&v1=a%2Bb%253D188%250Ac%2Bd%253D210%250Ae%2Bf%253D201%250Aa%2Bc%2Be%253D332%250Ad%2Bf%253D195%250Aa%2Be%253D232&v2=a%250Ab%250Ac%250Ad%250Ae%250Af`

```
x10=a ='t' [10th char of flag is t]
x11=b ='H'
x13=c ='d'
x15=d = 'n'
x16=e ='t'
x18=f ='U'
```

Final Flag:
UMDCTF-{I_L0v3_MatH_d0nt_Ufgh}