There are some large numbers here, since we are asked to answer in grams when the output is expressed in tons. The approach I'm taking is to calculate the number of moles 150 tons represents and then multiply that by 4 since we know we need 4 moles of H3BO3 for every mole of Na2B4O7 produced. Using the given conversion factors:
150 tons of Na2B4O7 is 1.36x108 grams.
The molar mass of Na2B4O7 is 201.2 g/mole, which means we have
6.77 x 105 moles of Na2B4O7
From the balanced equation, we need 4 times this number of moles:
2.71 x 106 moles of H3BO3 (That's the metric term for a lotta H3BO3)
At a molar mass of 61.8 g/mole for H3BO3 , we can multiply the moles times molar mass to get grams:
1.67 x 108 grams H3BO3