Please help! I need help finding the student's errors.
f(x)={x+3, x is less than of equal to -2}
{x^2-1, -2 is less than x is less than 1}
{log base 2 (-x+3), 1 is less than or equal to x is less than 3}

The function a represents the cost of manufacturing product a, in hundreds of dollars, and the function b represents the cost of manufacturing product b, in hundreds of dollars. a(t) = 5t + 2 b(t) = 7t - 2t +4 find the expression that describes the total cost of manufacturing both products, a(t) + b(t). a. 7t^2 - 7t + 2 b. 7t^2 + 3 +6 c. 7t^2 + 7t - 6 d. 7t^2 - 3t + 6