Answer:
A - 1:6
Step-by-step explanation:
a=5,b=10,c=15
1)(a+b)-5(c+a)
=(5+10)-5(15+5)
=(15)-5(20)
=15-5(20)
=10(20)
=200
2)(10×15)10(5×2)
=150×10×10
=15000
3)(a-b)+(a+b)
(5-10)+(10+5)
(-5)+15
-5+15
=10
4)(2ab-45)+a
=(2×5×10-45)+5
=(100-45)+5
=55+5
=60
