10 x {10: [10 - (10- a x 2)]} + 10 = 60
10 x {10: [10 - (10- a x 2)]} = 60-10
10 x {10: [10 - (10- a x 2)]} = 50
10: [10 - (10- a x 2)] = 50:10
10: [10 - (10- a x 2)] = 5
10 - (10- a x 2)= 5×10
10 - (10- a x 2)= 50
10 - a x 2= 10-50
10- a x 2= -40
a×2=10-(-40)
a×2=10+40
a×2=50
a=50:2
a=25