10y+$\frac{10x(28+1)}{2}$=155

y=1

=> (y+y+y+...+y)+(1+4+7+...+28)=155

xet tong 1+4+7+...+28 co: (28-1) /3+1=10 ( so hang)  => co 10 so hang y

=> 1+4+7+..+28=(1+28)*10/2=145

=) (y+1)+(y+4)+(y+7)+...+(y+28)=155

=>10y + 145=155

10y=155-145

10y=10

=> y=1

(Y+1)+(y+4)+(y+7)+……+(y+28)=155

=> (y + y + ... + y) + (1+ 4 + 7 + ... + 28)=155

=> 10 y + (1+28)+(4+25)+...+(13+16)=155

=> 10 y + 29 x 5 = 155

=> 10 y = 155 - 29 x5

=> 10y = 10

=> y=1

10y+fraction numerator 10 x left parenthesis 28 plus 1 right parenthesis over denominator 2 end fraction=155

y=1