a)
2⁷ + 2⁷ = 2 * 2⁷ = 2⁸
b)
5¹⁰ + 5¹⁰ + 5¹⁰ + 5¹⁰ + 5¹⁰ = 5 * 5¹⁰ = 5¹¹
c)
3 * (3¹⁵ + 3¹⁵ + 3¹⁵) = 3 * (3 * 3¹⁵) = 3 * 3¹⁶ = 3¹⁷